2) http://library.thinkquest.org/11353/trforest.htm
-Touches on A,B,C Tropical Rainforests: Equatorial Forests of Rain
Of all the world's forests, it is those in the tropics that face the greatest threat from mankind. Tropical rainforests are one of nature's treasures, and many of them are now at risk. We have already destroyed half of the world's original tropical rainforests! Just in a few decades, we can possibly witness the complete elimation of the world's rainforests. The biodiversity of this biome is legendary -- this biome contains the largest biomass. Did you know that enough rainforests are being destroyed every minute to fill 50 football fields? We need to preserve these valuable resources because they are the lungs of our planet, and can possibly hold cures for many of our most deadly diseases. The tropical rainforests are a critical link in the ecological chains of our our earth's biosphere. To learn more interesting facts about the tropical rainforests, please visit our Did you know? section.
Important Facts
Amazon rainforests produce about 40% of the world's oxygen
One in four pharmaceuticals comes from a plant in the tropical rainforests
1400 rainforest plants are believed to offer cures for cancer
40% of tropical rainforests have already been lost in Latin America and Southeast Asia
Technically, this type of forest can be defined as a forest in the tropics receiving 4-8 meters of rain each year. Tropical rainforests are found in Central and South America, Southeast Asia and islands near it, and West Africa. There are smaller rainforests in northern Australia and other small islands. All tropical rainforests are found along the equator where the temperatures and the humidity is always high, with the days being equal to the nights.
Eco-Joke
What do you call a parrot wearing a raincoat?
Answer: Polly Unsaturated
Generally, there is a flow of air that comes from the poles of the Earth, towards the equator. These winds are filled with moisture and the intense heat that is located at the equator causes the moisture to rise, cool and then condense to create rain. This continuous cycle causes it to rain almost 24 hours a day around most of the tropical areas. In some regions there can be more than 15 feet of rain a year. There are one or more "dry" months in this tropical biome, however if one would visit they would see it still is astonishingly wet.
Important Facts
Despite covering only 2% of our planet's surface, over half of the earth's animal, insect species, and flora live there.
Within a four mile square area of a tropical rainforest, you would find: * Over 750 species of trees
-"My personal love of the tropical forest is older than my realization of their scientific importance. It started when I lived for six months in the cathedral-like splendor of the forests of the upper Iriri in central Brazil, a shadowy world of great beauty without direct sunlight. That was then a region unexplored by Western man, teeming with wildlife, where you could push through dense undergrowth to broad rivers that had never been seen by any non-Indian.. More recently, on the Maraca Rainforest Project at the northern edge of the Amazon basin, I witnessed the amazing wealth of another uninhabited and undisturbed forest. We found several hundred species of creatures new to science - and indication of the amazing genetic wealth that remains to be discovered, and a reminder of the need to protect all types of forest. To protect the forests, we must protect the tribal people who have evolved a way of life in sustainable harmony with their habitat. I have studied the tragic history of countless tribes that have fought and suffered and are now extinct. During the two years that I have worked with Brazilian Indians, I have experienced the absolute quiet of sleeping in communal huts, fishing with Mehinaku, trying to keep up with walking Chavante, and the idyllic life in an Asurini village. Their struggle for survival must become our struggle too."-
John Hemming - Director and Secretary of the Royal Geographical Society in London
Wild and wondrous, rainforests extend from as far as Alaska and Canada to Latin America, Asia and Africa. They nurture thousands of plants and animals found nowhere else on Earth and provide life's essentials such as our medicines, food and water.
The Nature Conservancy is working around the world in places like Costa Rica's Osa Peninsula to protect rainforests, engaging local and indigenous communities in creative solutions that balance the needs of people with nature.
The places and projects featured on this site reflect examples of The Nature Conservancy's current work in rainforest protection. And every year, through our Adopt an Acre® program, we choose an imperiled rainforest site that is in critical need of protection.
Why Should You Care About the Rainforest?
Besides providing food, water and air to the rest of the world, rainforests offer critical habitat for many of the Earth's most interesting and rare plants and animals. Read on for more rainforest facts:
Temperate and tropical rainforests help regulate the Earth's temperature and weather patterns.
Rainforests provide jobs to surrounding communities.
Rainforests contain many of the essential plants used in the treatment of cancer.
Fifty percent of the world's plants and animals can be found in the rainforest.
The Nature Conservancy's Rainforests Work
The Nature Conservancy has launched many conservation programs to protect these vital forests and all the plants, animals and people that depend on them. Working in many of the world's most threatened forest systems, The Nature Conservancy has had many tangible and lasting successes:
Plant and animal diversity assessments of the coastal Amazon rainforest;
Training for national park guards in Bolivia;
Support for implementing rainforest protection projects in the Asia Pacific region;
Sustainable income-generating projects in Chile;
Effective park management in Panama and Costa Rica;
Scientific analysis of new protected areas within temperate rainforests in Canada; and
Since its beginning, our Adopt an Acre® program has protected hundreds of thousands of forested acres worldwide.
We are all part of this Earth. Invest in our future and the future of our planet. Be a steward of the rainforests.
When you make a gift to protect the rainforest, you'll help to ensure that the world’s most vital forests like the Osa are restored, protected and sustained for future generations.
Buy paper made from recycled materials. There's really no need to do otherwise, as recycled paper is available everywhere. Recycled paper often costs no more than regular paper.
Step 2
Participate in any recycling programs your local government has implemented. Place two garbage cans in your kitchen and encourage the family to sort recyclable paper products from general garbage. Your local waste management department may supply homes with special outdoor garbage cans for disposing of recyclable materials.
Step 3
Encourage recycling at your office. Talk to management about supplying recycling bins in addition to garbage cans. Circulate an office memo concerning conservation and recycling efforts.
Reduce Paper Usage to Save the Rainforest
Step 1
Turn to online news sources instead of printed hard copies of newspapers. Experts estimate that 30 million trees are cleared each year solely for the production of newspapers. Much of the trees used for newspapers come from tropical rainforest sources.
Step 2
Build a new home from materials other than trees. While American homes have been built from trees for generations, this has more to do with tradition than necessity. It's possible to build a home with little or no wood by using cob, rammed earth or PSP building techniques.
Step 3
Limit the amount of beef in your diet. It's estimated that 55 square feet of forest must be cleared to produce a single quarter-pound burger. While many fast food chains boast that they only use U.S. beef, the USDA only effectively labels where beef is processed and not where it's raised.
Step 4
Blow your nose into a washable handkerchief instead of tissue papers. Likewise, use towels and rags to clean your home instead of wasteful paper towels. Sacrifice a little convenience to help conserve our planet's rainforests.
Reuse Paper Whenever Possible
Step 1
Hang onto old pieces of junk mail. While you can't stop companies from wasting trees to produce ads that nobody reads, you can still put the paper to good use. Use old envelopes from credit offers to take phone messages or make "to do" lists.
Step 2
Wrap your Christmas presents in old newspapers. While colorful, shiny wrapping paper has been associated with the birth of Christ during modern times, there's no practical or Biblical justification for the practice. Use the Christmas season as an opportunity to help conserve our planet's precious natural resources.
5)http://www.wcupa.edu/aceer/rainforest.asp - Touches on B, C, D, and E Why Are Tropical Rainforests Important?
Tropical rainforests are the oldest and certainly the most complex ecosystems on our planet. They influence wind, rainfall, humidity and temperature patterns, and are a crucial link in the ecological chain of life—recycling water, oxygen, and carbon dioxide, and reducing soil erosion, flooding, and air contamination on a global scale.
Tropical rainforests play other important roles in our daily lives. Estimated to house almost half of the world’s plant, animal, and insect life, the forests are the Earth’s primary gene pool from which foods, medicine, and other products for the industrialized world are derived including coffee, tea, sugar, pepper, spices, bananas, rubber, and oils. Tropical rainforest plants already provide one-quarter of today’s pharmaceuticals and, according to The National Cancer Institute, a full 70% of the plants useful in the treatment of cancer are to be found only in our disappearing rainforest. How Much Rainforest Remains?
Tropical rainforest is disappearing faster than any other natural community on Earth. If we continue at our current rate of destruction, with population being the dominant factor, 70% of our remaining rainforests will by gone by the year 2050! Ancient forests, some of which have existed intact for seventy million years, since the days of the dinosaurs, will all but vanish. How Is The Rainforest Being Destroyed?
Every day about 90 acres of rainforest land is deforested.
A few thousand years ago, rainforests covered 14% of the earth’s land surface—5 billion acres. We have already destroyed a great deal of that. According to the United States National Academy of Sciences, more than 50 million acres of rainforest, an area the size of England, Scotland, and Wales, are destroyed or seriously degraded each year. Every day about 90 acres of rainforest land is deforested, creating infertile soil marked, ironically, for farming; for the creation of short-lived dams; for the mining of mineral resources; for cattle ranching to provide a cheaper fast-food hamburger for developed countries; for the importing of hardwood; and, most importantly, for the use of wood as fuel for cooking. The rainforest becomes a third-world commodity destined for transformation into paper bags, cardboard boxes, and hardwood floors. Whether for land or timber, deforestation of the world’s tropical rainforest has an appalling history of short-term benefits in exchange for irreversible loss. Why Won't The Rainforest Grow Back?
The complex and delicate relationships that have evolved over millions of years do not allow for independent survival. If the ecosystem of the world’s rainforest is destroyed, the stunning variety of plant and animal life we see today might never again regenerate. Without this complex system thriving above the soil, without nourishment from the roots and leaves of trees, the rainforest soil quickly becomes infertile. Crops planted on newly cleared land fail within a few years. Grasses planted for cattle refuse to seed and grow again. Without shade from the trees the earth is left dry, surrounding land flood from silt, and an eroded wasteland, emptied of the greatest diversity of life on Earth, is all that remains.
What is happening to the forest people?
What Is Happening To The Forest People?
Some tribes, well acquainted with the rainforest and its many resources, are disappearing from the forest due to outside influences new to the rainforest people. Foreign diseases and viruses, to which the forest people may have little resistance, can sweep through a tribe with devastating results. Tribal forest land is lost to loggers, ranchers, miners, and pioneer settlers who arrive in the forest with little understanding of the traditional agricultural methods that have sustained the tribes for centuries. Without their land, the forest people are absorbed into the new, dominant culture. With the disintegration of cultural identity, the tribe and all its working knowledge of the rainforest are swiftly lost. The people and their culture become extinct. What Are The Global Effects Of Deforestation?
The rainforest plays an integral support role for the planet. We know that on a regional basis deforestation results in soil loss, floods, drought, severe climatic changes, and the loss of a rich and bountiful habitat. We know also that the destruction of our tropical rainforest destroys the greatest storehouse of genetic diversity on Earth, a diversity that can provide new foods and medicines for the entire world. On a broader basis, the burning of the forests has been linked to increased carbon dioxide levels in our atmosphere, second only to that produced by the burning of fossil fuels. This well-documented increase in carbon dioxide levels is also associated with garbage dumping, changes in global climatic patterns, rising sea levels, and depletion of the protective ozone layer due to overpopulation. Consequently, action is needed now to protect what remains in our world’s rainforests. It is an important step toward the preservation of our future.
Edgar's work
Text 1: Answering point a). A tropical rainforest is an ecosystem usually found around the equator. They are common in Asia, Australia, Africa, South America, Central America, Mexico and on many of the Pacific Islands. Within the World Wildlife Fund's biome classification, tropical rainforests are considered a type of tropical wet forest (or tropical moist broadleaf forest) and may also be referred to as lowland equatorial evergreen rainforest. Minimum normal annual rainfall between 1,750 millimetres (69 in) and 2,000 millimetres (79 in) occurs in this climate region. Mean monthly temperatures exceed 18 °C (64 °F) during all months of the year.[1] Rainforests are home to half of all the living animal and plant species on the planet.[2] Tropical rain forests are called the "world's largest pharmacy" because over one-quarter of modern medicines originate from its plants.[3] The undergrowth in a rainforest is restricted in many areas by the lack of sunlight at ground level.[4] This makes it possible for people and other animals to walk through the forest. If the leaf canopy is destroyed or thinned for any reason, the ground beneath is soon colonized by a dense tangled growth of vines, shrubs and small trees called a jungle.
This was received from http://en.wikipedia.org/wiki/Tropical_rainforest.
Text 2: Answering point b). Tropical rainforests are unable to support human populations.[11] Food resources within the forest are extremely dispersed due to the high biological diversity and what food does exist is largely restricted to the canopy and requires considerable energy to obtain. Some groups of hunter-gatherers have exploited rainforest on a seasonal basis but dwelt primarily in adjacent savanna and open forest environments where food is much more abundant. Other peoples described as rainforest dwellers are hunter-gatherers who subsist in large part by trading high value forest products such as hides, feathers, and honey with agricultural people living outside the forest.[11]
[edit] Conversion to agricultural land
With the invention of agriculture humans were able to clear sections of rainforest to produce crops, converting it to open farmland. Such people, however, obtain their food primarily from farm plots cleared from the forest [11][12] and hunt and forage within the forest to supplement this.
Agriculture on formerly forested land is not without difficulties. Rainforest soils are often thin and leached of many minerals, and the heavy rainfall can quickly leach nutrients from area cleared for cultivation. People such as the Yanomamo of the Amazon, utilise slash-and-burn agriculture to overcome these limitations and enable them to push deep into what were previously rainforest environments. However, these are not rainforest dwellers, rather they are dwellers in cleared farmland[11][13] that make forays into the rainforest and up to 90% of the typical Yanamomo diet comes from farmed plants.[14]
[edit] Cultivated foods and spices
Coffee, chocolate, banana, mango, papaya, macadamia, avocado, and sugarcane all originally came from tropical rainforest and are still mostly grown on plantations in regions that were formerly primary forest. In the mid-1980s and 90s, 40 million tons of bananas were consumed worldwide each year, along with 13 million tons of mangoes. Central American coffee exports were worth US$3 billion in 1970. Much of the genetic variation used in evading the damage caused by new pests is still derived from resistant wild stock. Tropical forests have supplied 250 cultivated kinds of fruit, compared to only 20 for temperate forests. Forests in New Guinea alone contain 251 tree species with edible fruits, of which only 43 had been established as cultivated crops by 1985.[15]
[edit] Pharmaceutical and biodiversity resource
Tropical rainforests are called "the world's largest pharmacy"[citation needed] because of the large amount of natural medicines discovered in rainforests that are derived from rainforest plants. For example, rain forests contain the "basic ingredients of hormonal contraception methods, cocaine, stimulants, and tranquilizing drugs" (Banks 36)[citation needed]. Curare (a paralyzing drug) and quinine (a malaria cure) are also found there.
[edit] Tourism
Tourism in tropical rainforests has increased over the years having both positive and negative effects.[citation needed] People travel both nationally and internationally to experience rain forests firsthand.
[edit] Positive Impacts Onset dates and prevailing wind currents of the southwest summer monsoon.
Despite the negative effects of tourism in the tropical rainforests, there are also several important positive effects. * An increase in tourism has increased economic support, allowing more revenue to go into the protection of the habitat. Tourism can contribute directly to the conservation of sensitive areas and habitat. Revenue from park-entrance fees and similar sources can be utilised specifically to pay for the protection and management of environmentally sensitive areas. Revenue from taxation and tourism provides an additional incentive for governments to contribute revenue to the protection of the forest. * Tourism also has the potential to increase public appreciation of the environment and to spread awareness of environmental problems when it brings people into closer contact with the environment. Such increased awareness can induce more environmentally conscious behavior. Tourism has had a positive effect on wildlife preservation and protection efforts, notably in Africa but also in South America, Asia, Australia, and the South Pacific.[16] This website was also received from the one above.
Text 3: Answering point c).
The Disappearing Rainforests ·We are losing Earth's greatest biological treasures just as we are beginning to appreciate their true value. Rainforests once covered 14% of the earth's land surface; now they cover a mere 6% and experts estimate that the last remaining rainforests could be consumed in less than 40 years. ·One and one-half acres of rainforest are lost every second with tragic consequences for both developing and industrial countries. ·Rainforests are being destroyed because the value of rainforest land is perceived as only the value of its timber by short-sighted governments, multi-national logging companies, and land owners. ·Nearly half of the world's species of plants, animals and microorganisms will be destroyed or severely threatened over the next quarter century due to rainforest deforestation. ·Experts estimates that we are losing 137 plant, animal and insect species every single day due to rainforest deforestation. That equates to 50,000 species a year. As the rainforest species disappear, so do many possible cures for life-threatening diseases. Currently, 121 prescription drugs sold worldwide come from plant-derived sources. While 25% of Western pharmaceuticals are derived from rainforest ingredients, less that 1% of these tropical trees and plants have been tested by scientists. ·Most rainforests are cleared by chainsaws, bulldozers and fires for its timber value and then are followed by farming and ranching operations, even by world giants like Mitsubishi Corporation, Georgia Pacific, Texaco and Unocal. ·There were an estimated ten million Indians living in the Amazonian Rainforest five centuries ago. Today there are less than 200,000. ·In Brazil alone, European colonists have destroyed more than 90 indigenous tribes since the 1900's. With them have gone centuries of accumulated knowledge of the medicinal value of rainforest species. As their homelands continue to be destroyed by deforestation, rainforest peoples are also disappearing. ·Most medicine men and shamans remaining in the Rainforests today are 70 years old or more. Each time a rainforest medicine man dies, it is as if a library has burned down. ·When a medicine man dies without passing his arts on to the next generation, the tribe and the world loses thousands of years of irreplaceable knowledge about medicinal plants. This text was received from http://www.rain-tree.com/facts.htm.
Text 4: Answering point a). -The Amazon Rainforest covers over a billion acres, encompassing areas in Brazil, Venezuela, Colombia and the Eastern Andean region of Ecuador and Peru. If Amazonia were a country, it would be the ninth largest in the world. -More than half of the world's estimated 10 million species of plants, animals and insects live in the tropical rainforests. -One hectare (2.47 acres) may contain over 750 types of trees and 1500 species of higher plants. This text was from the same source as above.
Text 5: Answering to point b). -The Amazon Rainforest has been described as the "Lungs of our Planet" because it provides the essential environmental world service of continuously recycling carbon dioxide into oxygen. More than 20 percent of the world oxygen is produced in the Amazon Rainforest. -One-fifth of the world's fresh water is in the Amazon Basin. -At least 80% of the developed world's diet originated in the tropical rainforest. Its bountiful gifts to the world include fruits like avocados, coconuts, figs, oranges, lemons, grapefruit, bananas, guavas, pineapples, mangos and tomatoes; vegetables including corn, potatoes, rice, winter squash and yams; spices like black pepper, cayenne, chocolate, cinnamon, cloves, ginger, sugar cane, tumeric, coffee and vanilla and nuts including Brazil nuts and cashews. -Rainforest plants are rich in secondary metabolites, particularly alkaloids. Biochemists believe alkaloids protect plants from disease and insect attacks. Many alkaloids from higher plants have proven to be of medicinal value and benefit. -Currently, 121 prescription drugs currently sold worldwide come from plant-derived sources. And while 25% of Western pharmaceuticals are derived from rainforest ingredients, less than 1% of these tropical trees and plants have been tested by scientists. -The U.S. National Cancer Institute has identified 3000 plants that are active against cancer cells. 70% of these plants are found in the rainforest. Twenty-five percent of the active ingredients in today's cancer-fighting drugs come from organisms found only in the rainforest. -Vincristine, extracted from the rainforest plant, periwinkle, is one of the world's most powerful anticancer drugs. It has dramatically increased the survival rate for acute childhood leukemia since its discovery. -In 1983, there were no U.S. pharmaceutical manufacturers involved in research programs to discover new drugs or cures from plants. Today, over 100 pharmaceutical companies and several branches of the US government, including giants like Merck and The National Cancer Institute, are engaged in plant research projects for possible drugs and cures for viruses, infections, cancer, and even AIDS. This text was received from the same source as above.
Text 6: Answering to point d). Due to their positioning in the monsoon regions of the Earth, the Rainforests attract heavy rainfall and absorb
large quantities of carbon dioxide and emit oxygen into the atmosphere. Due to the Earth’s tilt, the Rainforests are
situated in a region of the Earth that gets regular sunlight. As the rain falls in this region, it helps to cool the Earth. This in
turn causes a climate within a climate as the humidity creates moisture, which is condensed into clouds. The rains then
return to the forests to be taken up by the trees and plants. This cycle is ever repeating and it cools the Earth, and also
creates lush green environments in these areas.
To mention the Earth's tilt again. The Earth's tilt in axis of rotation is normally 23.5 degrees from the
perpendicular to the orbit plane. But the Earth's tilt is out by 5 more degrees causing instability within the core. If all of
the Rainforests are destroyed by 2012, then there is no way this error can be corrected. We must start replanting NOW to
stop the environmental catastrophe that will befall us. The Rainforests have more of a role in balancing the Earth’s temperatures than we realise, both internally and
externally, controlling the Earth’s winds and believe it or not, the temperature of the Seas. The Rainforests also keep the pattern of the winds to the northern and southern hemispheres. With the rainforests being
destroyed, these winds are changing their direction, spreading disease to other parts of the Earth and coupled with
warmer temperatures, the rain is unlikely to fall in sufficient quantities in the right places that would cool the Earth. These
areas would then be more prone to flash floods and mudslides. With changing wind patterns, the temperature of the seas
would not be able to be kept constant. The Earth maintains an equilibrium but our actions are hampering its efforts ! Some scientists argue that these are natural changes and that there is nothing to worry about, but these
changes are the result of global warming and whether a natural occurrence or not, has most definitely been accelerated
by Man due to an increasing reliance on fossil fuels – It is reported by scientists that in the last 450,000 years,
carbon dioxide (produced from the combustion of fossil fuels) has not risen as much as it has since the
Industrial revolution! This text was received from http://www.saveourearth.co.uk/downloads/leaflet.pdf.
The world's tropical forests circle the globe in a ring around the Equator They are surprisingly diverse, ranging from lush rain forests to dry savannas and containing millions of species of plants and animals (fig. 1). Tropical forests once covered some 15.3 billion acres (6.2 billion ha). In recent times, however, they have been cut at a rapid rate to make room for agriculture and to obtain their many valuable products. Between 1985 and 1990, 210 million acres (85 million ha) of tropical forests were destroyed.
This guide shows how modern forest practices can help stem the tide of forest destruction while providing valuable forest products for people. The tropical forests of Puerto Rico, which were abused for centuries, were badly depleted by the early 1900's. Widespread abandonment of poor agricultural lands has allowed natural reforestation and planting programs to create a patchwork of private, Commonwealth, and Federal forests across the land (fig. 2). The most frequent example in this publication is the Luquillo Experimental Forest, which could be a model for protecting and managing tropical forests worldwide. About half of all the world's forests are in the Tropics, the area between the Tropic of Cancer and the Tropic of Capricorn. This region may be best known for its rain forests - lush, steamy jungles with towering trees, epiphytes, and dense under stories of smaller trees, shrubs, and vines. Tropical forests are surprisingly diverse. In addition to rain forests, there are mangroves, moist forests, dry forests, and savannas. Such classifications, however, give only a slight indication of the diversity of tropical forests. One study by the Food and Agriculture Organization (FAO) of the United Nations, which considered 23 countries in tropical America, 37 in tropical Africa, and 16 in tropical Asia, identified dozens of types of tropical forests: open and closed canopy forests, broadleaved trees and conifer forests , closed forests and mixed forest grasslands, and forests where agriculture has made inroads. Rain Forests The largest remaining areas of tropical rain forests are in Brazil, Congo, Indonesia, and Malaysia. Precipitation generally exceeds 60 inches (150 cm) per year and may be as high as 400 inches (1000 cm). Lowland rain forests are among the world's most productive of plant communities. Giant trees may tower 200 feet (60 m) in height and support thousands of other species of plants and animals. Montane (mountain) rain forests grow at higher elevations where the climate is too windy and wet for optimum tree growth. Mangrove forests grow in the swampy, intertidal margin between sea and shore and are often considered part of the rain forest complex. The roots of mangrove trees help stabilize the shoreline and trap sediment and decaying vegetation that contribute to ecosystem productivity (fig. 3). Dry Forests Large areas of tropical dry forests are found in India, Australia, Central and South America, the Caribbean, Mexico, Africa, and Madagascar. Dry forests receive low rainfall amounts, as little as 20 inches (50 cm) per year, and are characterized by species well adapted to drought. Trees of dry tropical forests are usually smaller than those in rain forests, and many lose their leaves during the dry season. Although they are still amazingly diverse, dry forests often have fewer species than rain forests. Savanna is a transitional type between forest and grassland. Trees are often very scattered and tend to be well adapted to drought and tolerant of fire and grazing. If fire is excluded, trees eventually begin to grow and the savanna is converted to dry forest. With too much fire or grazing, dry forest becomes savanna (fig. 4). This vegetation type has fewer species of trees and shrubs but more grasses and forbs than other forest types in the Tropics.
All forests have both economic and ecological value, but tropical forests are especially important in global economy. These forests cover less than 6 percent of the Earth's land area, but they contain the vast majority of the world's plant and animal genetic resources. The diversity of life is astonishing. The original forests of Puerto Rico, for example, contain more than 500 species of trees in 70 botanical families. By comparison, temperate forests have relatively few. Such diversity is attributed to variations in elevation, climate, and soil, and to the lack of frost. There is also diversity in other life forms: shrubs, herbs, epiphytes, mammals, birds, reptiles, amphibians, and insects. One study suggests that tropical rain forests may contain as many as 30 million different kinds of plants and animals, most of which are insects (fig. 5). Wood and Other Products Tropical forests provide many valuable products including rubber, fruits and nuts, meat, rattan, medicinal herbs, floral greenery, lumber, firewood, and charcoal. Such forests are used by local people for subsistence hunting and fishing. They provide income and jobs for hundreds of millions of people in small, medium, and large industries. Tropical forests are noted for their beautiful woods (fig. 6). Four important commercial woods are mahogany, teak, melina, and okoume. Honduras mahogany (Swietenia macrophylla), grows in the Americas from Mexico to Bolivia. A strong wood of medium density, mahogany is easy to work, is long lasting, and has good color and grain. It is commonly used for furniture, molding, paneling, and trim. Because of its resistance to decay, it is a popular wood used in boats. Teak (Tectona grandis) is native to India and Southeast Asia. Its wood has medium density, is strong, polishes well, and has a warm yellow-brown color. Also prized for resistance to insects and rot, teak is commonly used in cabinets, trim, flooring, furniture, and boats (fig. 7). Melina (Gmelina arborea) grows naturally from India through Vietnam. Noted for fast growth, melina has light colored wood that is used mainly for pulp and particleboard, matches and carpentry. Okoume (Aucoumea klaineana) is native to Gabon an the Congo in west Africa. A large fast-growing tree, the wood has mod erately low density, good strength-to density ratio, and low shrinkage during drying. It is commonly use( for plywood, paneling, interior fur niture parts, and light construction. Other Economic Values Tropical forests are home for tribal hunter-gatherers whose way of life has been relatively unchanged for centuries. These people depend on the forests for their livelihood. More than 2.5 million people also live in areas adjacent to tropical forests. They rely on the forests for their water, fuelwood, and other resources and on its shrinking land base for their shifting agriculture. For urban dwellers, tropical forests provide water for domestic use and hydroelectric power. Their scenic beauty, educational value, and opportunities for outdoor recreation support tourist industries. Many medicines and drugs come from plants found only in tropical rain forests. Some of the best known are quinine, an ancient drug used for malaria; curare, an anesthetic and muscle relaxant used in surgery; and rosy periwinkle, a treatment for Hodgkin's disease and leukemia. Research has identified other potential drugs that may have value as contraceptives or in treating a multitude of maladies such as arthritis, hepatitis, insect bites, fever, coughs, and colds. Many more may be found. In all, only a few thousand species have been evaluated for their medicinal value. In addition, many plants of tropical forests find uses in homes and gardens: ferns and palms, the hardy split-leaf philodendron, marantas, bromeliads, and orchids (fig. 8), to name just a few. Environmental Benefits Tropical forests do more than respond to local climatic conditions; they actually influence the climate. Through transpiration, the enormous number of plants found in rain forests return huge amounts of water to the atmosphere, increasing humidity and rainfall, and cooling the air for miles around. In addition, tropical forests replenish the air by utilizing carbon dioxide and giving off oxygen. By fixing carbon they help maintain the atmospheric carbon dioxide levels low and counteract the global "greenhouse" effect. Forests also moderate stream flow. Trees slow the onslaught of tropical downpours, use and store vast quantities of water, and help hold the soil in place. When trees are cleared, rainfall runs off more quickly, contributing to floods and erosion.
Before the dawn of agriculture approximately 10,000 years ago, forests and open woodland covered about 15.3 billion acres (6.2 billion ha) of the globe. Over the centuries, however, about one-third of these natural forests has been destroyed. According to a 1982 study by FAO, about 27.9 million acres (11.3 million ha) of tropical forests are cut each year-an area about the size of the States of Ohio or Virginia. Between 1985 and 1990, an estimated 210 million acres (85 million ha) of tropical forests were cut or cleared. In India, Malaysia, and the Philippines, the best commercial forests are gone, and cutting is increasing in South America. If deforestation is not stopped soon, the world will lose most of its tropical forests in the next several decades. Reasons for Deforestation Several factors are responsible for deforestation in the Tropics: clearing for agriculture, fuelwood cutting, and harvesting of wood products. By far the most important of these is clearing for agriculture. In the Tropics, the age-old practice of shifting, sometimes called "slash-and-burn," agriculture has been used for centuries. In this primitive system, local people cut a small patch of forest to make way for subsistence farming. After a few years, soil fertility declines and people move on, usually to cut another patch of trees and begin another garden. In the abandoned garden plot, the degraded soil at first supports only weeds and shrubby trees. Later, soil fertility and trees return, but that may take decades. As population pressure increases, the fallow (rest) period between cycles of gardening is shortened, agricultural yields decrease, and the forest region is further degraded to small trees, brush, or eroded savanna. Conversion to sedentary agriculture is an even greater threat to tropical forests. Vast areas that once supported tropical forests are now permanently occupied by subsistence farmers and ranchers and by commercial farmers who produce sugar, cocoa, palm oil, and other products. In many tropical countries there is a critical shortage of firewood. For millions of rural poor, survival depends on finding enough wood to cook the evening meal. Every year more of the forest is destroyed, and the distance from home to the forest increases. Not only do people suffer by having to spend much of their time in the search for wood, but so does the land. Damage is greatest in dry tropical forests where firewood cutting converts forests to savannas and grasslands. The global demand for tropical hardwoods, an $8-billion-a-year industry, also contributes to forest loss. Tropical forests are usually selectively logged rather than clear-cut. Selective logging leaves the forest cover intact but usually reduces its commercial value because the biggest and best trees are removed. Selective logging also damages remaining trees and soil, increases the likelihood of fire, and degrades the habitat for wildlife species that require large, old trees-the ones usually cut. In addition, logging roads open up the forests to shifting cultivation and permanent settlement. In the past, logging was done primarily by primitive means-trees were cut with axes and logs were moved with animals such as oxen. Today the use of modern machinery--chain saws, tractors, and trucks -makes logging easier, faster, and potentially more destructive. Endangered Wildlife Forests are biological communities-complex associations of trees with other plants and animals that have evolved together over millions of years. Because of the worldwide loss of tropical forests, thousands of species of birds and animals are threatened with extinction. The list includes many unique and fascinating animals, among them the orangutan, mountain gorilla, manatee, jaguar, and Puerto Rican parrot. Although diverse and widely separated around the globe, these specles have one important thing in common. They, along with many other endangered species, rely on tropical forests for all or part of their habitat. Orangutans (Pongo pygmaeus) are totally dependent on small and isolated patches of tropical forests remaining in Borneo and Sumatra, Indonesia. Orangutans spend most of their time in the forest canopy where they feed on leaves, figs and other fruit, bark, nuts, and insects. Large trees of the old-growth forests support woody vines that serve as aerial ladders, enabling the animals to move about, build their nests, and forage for food. When the old forests are cut, orangutans disappear. The largest of all primates, the gorilla, is one of man's closest relatives in the animal kingdom. Too large and clumsy to move about in the forest canopy, the gorilla lives on the forest floor where it forages for a variety of plant materials. Loss of tropical forests in central and west Africa is a major reason for the decreasing numbers of mountain gorillas (Gorilla gorilla). Some habitat has been secured, but the future of this gentle giant is in grave danger as a result of habitat loss and poaching. The jaguar (Leo onca), a resident of the Southwestern United States and Central and South America, is closely associated with forests. Its endangered status is the result of hunting and habitat loss. The Puerto Rican parrot (Amazona vittata), a medium-sized, green bird with blue wing feathers, once inhabited the entire island of Puerto Rico and the neighboring islands of Mona and Culebra. Forest destruction is the principal reason for the decline of this species. Hunting also contributed. Today, only a few Puerto Rican parrots remain in the wild and their survival may depend on the success of a captive breeding program (fig. 9). In addition to species that reside in tropical forests year round, others depend on such forests for part of the year. Many species of migrant birds journey 1,000 miles or more between their summer breeding grounds in the north and their tropical wintering grounds. These birds are also threatened by tropical forest destruction.
All the world's forests, it is those in the tropics that face the greatest threat from mankind. Tropical rainforests are one of nature's treasures, and many of them are now at risk. We have already destroyed half of the world's original tropical rainforests! Just in a few decades, we can possibly witness the complete elimation of the world's rainforests. The biodiversity of this biome is legendary -- this biome contains the largest biomass. Did you know that enough rainforests are being destroyed every minute to fill 50 football fields? We need to preserve these valuable resources because they are the lungs of our planet, and can possibly hold cures for many of our most deadly diseases. The tropical rainforests are a critical link in the ecological chains of our our earth's biosphere. To learn more interesting facts about the tropical rainforests, please visit our Did you know? section.
Important Facts
Amazon rainforests produce about 40% of the world's oxygen
One in four pharmaceuticals comes from a plant in the tropical rainforests
1400 rainforest plants are believed to offer cures for cancer
40% of tropical rainforests have already been lost in Latin America and Southeast Asia
Technically, this type of forest can be defined as a forest in the tropics receiving 4-8 meters of rain each year. Tropical rainforests are found in Central and South America, Southeast Asia and islands near it, and West Africa. There are smaller rainforests in northern Australia and other small islands. All tropical rainforests are found along the equator where the temperatures and the humidity is always high, with the days being equal to the nights.
Generally, there is a flow of air that comes from the poles of the Earth, towards the equator. These winds are filled with moisture and the intense heat that is located at the equator causes the moisture to rise, cool and then condense to create rain. This continuous cycle causes it to rain almost 24 hours a day around most of the tropical areas. In some regions there can be more than 15 feet of rain a year. There are one or more "dry" months in this tropical biome, however if one would visit they would see it still is astonishingly wet.
Important Facts
Despite covering only 2% of our planet's surface, over half of the earth's animal, insect species, and flora live there.
Within a four mile square area of a tropical rainforest, you would find: * Over 750 species of trees
Rainforests are important to the global ecosystem. Rainforests:
provide a home to many plants and animals;
help stabilize the world's climate;
protect against flood, drought, and erosion;
are a source for medicines and foods;
support tribal people; and
are an interesting place to visit
Rainforests help stabilize the world's climate by absorbing carbon dioxide from the atmosphere. Excess carbon dioxide in the atmosphere is believed to contribute to climate change through global warming. Therefore rainforests have an important in addressing global warming.
Rainforests also affect local weather conditions by creating rainfall and moderating temperatures.
Rainforests help stabilize the world's climate by absorbing carbon dioxide from the atmosphere. Excess carbon dioxide in the atmosphere is believed to contribute to climate change through global warming. Therefore rainforests have an important in addressing global warming.
Rainforests also affect local weather conditions by creating rainfall and moderating temperatures.
Rainforests help maintain the water cycle. According to the U.S. Geological Survey, "the water cycle, also known as the hydrologic cycle, describes the continuous movement of water on, above, and below the surface of the Earth."
The role of rainforests in the water cycle is to add water to the atmosphere through the process of transpiration (where they release water from their leaves during photosynthesis). This moisture contributes to the formation of rain clouds which release the water back on the rainforest. In the Amazon, 50-80% of moisture remains in the ecosystem's water cycle.
When the forests are cut down, less moisture is goes into the atmosphere and rainfall declines and sometimes leads to drought.
The roots of rainforest trees and vegetation help anchor the soil. When trees are cut down there is no longer anything to protect the ground and soils are quickly washed away with rain. The process of washing away of soil is known as erosion.
As soil is washed down into rivers it causes problems for fish and people. Fish suffer because water becomes clouded, while people have trouble navigating waterways that are shallower because of the increased amount of dirt in the water. Meanwhile farmers lose topsoil that is important for growing crops.
Website 4: www.en.wikipedia.org
Habitation
Tropical rainforests are unable to support human populations.[11] Food resources within the forest are extremely dispersed due to the high biological diversity and what food does exist is largely restricted to the canopy and requires considerable energy to obtain. Some groups of hunter-gatherers have exploited rainforest on a seasonal basis but dwelt primarily in adjacent savanna and open forestenvironments where food is much more abundant. Other peoples described as rainforest dwellers are hunter-gatherers who subsist in large part by trading high value forest products such as hides, feathers, and honey with agricultural people living outside the forest.[11] Conversion to agricultural land
With the invention of agriculture humans were able to clear sections of rainforest to produce crops, converting it to open farmland. Such people, however, obtain their food primarily from farm plots cleared from the forest [11][12] and hunt and forage within the forest to supplement this.
Agriculture on formerly forested land is not without difficulties. Rainforest soils are often thin and leached of many minerals, and the heavy rainfall can quickly leach nutrients from area cleared for cultivation. People such as the Yanomamo of the Amazon, utilise slash-and-burn agriculture to overcome these limitations and enable them to push deep into what were previously rainforest environments. However, these are not rainforest dwellers, rather they are dwellers in cleared farmland[11][12] that make forays into the rainforest and up to 90% of the typical Yanamomo diet comes from farmed plants.[12] Cultivated foods and spices Coffee, chocolate, banana, mango, papaya, macadamia, avocado, and sugarcane all originally came from tropical rainforest and are still mostly grown on plantations in regions that were formerly primary forest. In the mid-1980s and 90s, 40 million tons of bananas were consumed worldwide each year, along with 13 million tons of mangoes. Central American coffee exports were worth US$3 billion in 1970. Much of the genetic variation used in evading the damage caused by new pests is still derived from resistant wild stock. Tropical forests have supplied 250 cultivated kinds of fruit, compared to only 20 for temperate forests. Forests in New Guinea alone contain 251 tree species with edible fruits, of which only 43 had been established as cultivated crops by 1985.[13] Pharmaceutical and biodiversity resource
Tropical rainforests are called "the world's largest pharmacy"[citation needed] because of the large amount of natural medicines discovered in rainforests that are derived from rainforest plants. For example, rain forests contain the "basic ingredients of hormonal contraception methods, cocaine, stimulants, and tranquilizing drugs" (Banks 36)[citation needed]. Curare (a paralyzing drug) and quinine (a malaria cure) are also found there. Tourism Tourism in tropical rainforests has increased over the years having both positive and negative effects.[citation needed] People travel both nationally and internationally to experience rain forests firsthand.
Positive Impacts
Onset dates and prevailing wind currents of the southwest summer monsoon.
Despite the negative effects of tourism in the tropical rainforests, there are also several important positive effects.
An increase in tourism has increased economic support, allowing more revenue to go into the protection of the habitat. Tourism can contribute directly to the conservation of sensitive areas and habitat. Revenue from park-entrance fees and similar sources can be utilised specifically to pay for the protection and management of environmentally sensitive areas. Revenue from taxation and tourism provides an additional incentive for governments to contribute revenue to the protection of the forest.
Tourism also has the potential to increase public appreciation of the environment and to spread awareness of environmental problems when it brings people into closer contact with the environment. Such increased awareness can induce more environmentally conscious behavior. Tourism has had a positive effect on wildlife preservation and protection efforts, notably in Africa but also in South America, Asia, Australia, and the South Pacific.[14]
Ecosystem services
In addition to extractive human uses rain forests also have non-extractive uses that are frequently summarized as ecosystem services. Rain forests play an important role in maintaining biological diversity, modulating precipitation, infiltration and flooding, increasing scientific knowledge and in the spiritual well-being of humans. Such ecosystem services are of use to humans without the need for any modification or management of the forest yourself.
Often described as the Earth’s lungs, only in reverse, the tropical rainforests, take in vast quantities of carbon dioxide (a poisonous gas which mammals exhale) and through the process of photosynthesis, converts it into clean, breathable air. In fact, the tropical rainforests are the single greatest terrestrial source of air that we breathe.
What’s truly amazing, however, is that while the tropical rainforests cover just 2% of the Earth's land surface, they are home to two-thirds of all the living species on the planet. Additionally, "nearly half the medicinal compounds we use every day come from plants endemic to the tropical rainforest." If a cure for cancer or AIDS is to be found, it’ll almost certainly come from the tropical rainforests.
Norman Myers, in his book, The Primary Source, writes that "tropical rainforests are the Earth’s oldest continuous ecosystems. Fossil records show that the forests of Southeast Asia have existed in more or less their present form for 70 to 100 million years. The intensity of life forms is extraordinary: on the order of 1,000 species per square kilometer. By comparison, here in North America, we might only find 100 species in the same space." (2)
The largest rainforests are found in the Amazon Basin of South America, in Western African countries that skirt the equator, as well as South Pacific countries such as Indonesia and the Philippines. Smaller tracts of rainforests exist throughout Central America, parts of Mexico and Hawaii, as well as other islands of the Pacific and Caribbean.
Circling the Earth’s equator like a belt, the tropical rainforests maintain a near constant temperature of 80 degrees Fahrenheit and receive anywhere from 160 to 400 inches of rain per year. These favorable weather conditions allow all life forms to flourish year- round. Furthermore, by virtue of their location, the tropical rainforests were spared the extreme loss of life that characterized other regions of the globe during the ice ages. These two factors help explain why the tropical rainforests are home to between 50 and 70 million different life forms.
Tragically, the tropical rainforests are being destroyed at an alarming rate. According to Rainforest Action Network, more than an acre-and-a-half is lost every second of every day (refer to the entries below to see, quantitatively, what that translates into). That’s an area more than twice the size of Florida that goes up in smoke every year! "If present rates of destruction continue, half our remaining rainforests will be gone by the year 2025, and by 2060 there will be no rainforests remaining."
Every second . . we lose an area the size of two football fields!
Every minute . . we lose an area 29 times the size of the Pentagon!
Every hour . . . we lose an area 684 times larger than the New Orleans Superdome!
Every day . . . we lose an area larger than all five boroughs of New York City!
Every week . . . we lose an area twice the size of Rhode Island!
Every month . . .we lose an area the size of Belize!
Every year . . . we lose an area more than twice the size of Florida!
At the very least, "with the destruction of the tropical rainforests, over half the plant and animal species on earth, as well as numerous indigenous cultures will disappear forever."(2) If strong and decisive action is not taken immediately to reverse the destruction of this vital ecosystem, the consequences will be catastrophic. In fact, many scientists agree that the earth could very well become uninhabitable for virtually every living species, including humans!
We’ve consulted some knowledgeable experts in the field of tropical rainforest conservation and come up with some sobering facts that will lend credence for taking immediate action to save the last remaining tropical rainforests. And what might happen if we don’t.
B I O - D I V E R S I T Y
. . . "a typical four-mile square mile patch of rainforest contains as many as 1,500 species of flowering plants, 750 species of trees, 125 mammal species, 400 species of birds, 100 species of reptiles, 60 species of amphibians, and 150 different species of butterflies."
. . . "there are more fish species in the Amazon river system than in the entire Atlantic Ocean."
. . . "a single rainforest reserve in Peru is home to more species of birds than the entire United States."
. . . "at least 1/3 of the planet’s bird species live in the Amazon rainforest."
. . ."the Andean mountain range and the Amazon jungle are home to more than half of the world’s species of flora and fauna."
. . . "at least 1,650 rainforest plants can be utilized as alternatives to our present fruit and vegetable staples."
. . . "37% of all medicines prescribed in the US have active ingredients derived from rainforest plants."
. . . "70% of the plant species identified by the US National Cancer Institute as holding anti-cancer properties come from rainforests."
. . . "90% of the rainforest plants used by Amazonian Indians as medicines have not been examined by modern science."
. . . "of the few rainforest plant species that have been studied by modern medicine, treatments have been found for childhood leukemia, breast cancer, high blood pressure, asthma, and scores of other illnesses."
. . . "a hectare (2.471 acres) of rainforest absorbs one ton of carbon dioxide (CO2) per year."
. . . conversely, "the clearing and burning of the world’s rainforest accounts for 20-25% of the CO2 emitted into the atmosphere by man. It therefore could play a significant role in any so called "greenhouse effect" underway in our atmosphere."
THE COST OF RAINFOREST DESTRUCTION
. . . "almost half of the world’s original four billion acres of rainforest are now gone. The lost area equals the combined size of Washington, Idaho, California, Nevada and Arizona."
. . . "in 1500, there were an estimated six to nine million indigenous people inhabiting the tropical rainforests of Brazil. By 1900, that number had dropped to a million. Today, there are less than 250,000 indigenous people left in Brazil."
. . . "man has recently increased nature’s "normal" extinction rate by 10,000%. Most of this increase is taking place in the rainforests."
. . . "by conservative estimates, 9,000 species are going extinct each year, most of them from the rainforests."
. . . "we are presently experiencing the largest mass extinction since the demise of the dinosaurs 65 million years ago; only this time it’s occurring at a much faster rate."
Website 6: http://www.accu.or.jp/litdbase/material/pdf2/mt/mt09/mt09_06.pdf
"... the most complex ecosystem on earth ... the tropical rain forest is one thousand times more biologically complex than the tropical reef system, the second most complex system on earth, with one million times greater biodiversity than our own ecosystem here." - Mike Robinson, Director of National ZooIntroduction
In previous lectures we focused on general principles of ecosystems, emphasizing the processes of biogeochemical cycling and energy transfers. In the next lectures we will look at one ecosystem in detail, the tropical forest. There are several reasons for this. Ecosystems may all function according to the same basic principles, but they most certainly don't all look the same and it is important to have some understanding and appreciation of this diversity. Second, it is important to learn about the "specifics" of ecosystems as well as the "generalities". Finally, we can use this examination of the tropical forest to help tie together some of the material that has been presented in the ecology and evolution sections of the course. Today we will examine the most productive and diverse ecosystem found on land: the tropical rain forest. These ecosystems are also, and perhaps more accurately, called humid tropical forests. These ecosystems are also changing rapidly, as Figure 1 illustrates in terms of the past and present distribution of tropical forests on earth. Climate and Geography Certain ranges of temperature and rainfall characterize the places where tropical rainforests occur:
Temperatures generally fall between 23 - 27 deg C, with a greater daily than monthly range. In other words, there is no strong seasonality of temperature (unlike what we experience in Michigan). Rainfall tends to be highest near the equator, where the sun's evaporative power causes high evapotranspiration, and rising air cools and then sheds its moisture. Precipitation tapers off as one moves away from the equator, and dry belts are found at 25-30 deg of latitude. Local variation can also be great due to trade winds, ocean currents, land masses, and mountain ranges. Evergreen forests are replaced by deciduous forests as precipitation becomes seasonal. Wherever dry periods are several months or longer in duration, leaves are shed as the dry season takes hold, providing a winter-like visual appearance. Leaves re-appear in anticipation of or with the onset of the rains. (A dry month is one where evapotranspiration exceeds precipitation.) The growing season is thus shortened, and so forest productivity is less than in the evergreen forests of the more humid tropics. At lower annual rainfall (ca. 1500 mm), forest gives way to savanna as can be seen in the vegetation map of Africa in Figure 2. Boundaries between ecosystems or biomes are often gradual, and they can be sensitive to changing conditions. A prolonged period of wetness or drought, or human intervention, can cause dramatic changes because of the transitional nature of environmental conditions near the boundaries between biomes. Humid tropical forests appear superficially similar everywhere, but in fact they differ widely in species composition and ecosystem attributes. In the coterminous United States, botanists recognize 135 natural plant formations based on dominant species, and driven by latitude and climate. This system is called the Holdridge system (Figure 3) and it is widely used for conservation purposes. However, its use is far from feasible in tropics. Instead, the future in classifying tropical rainforest plant formations may lie in remote sensing, where large areas can be mapped relatively quickly. Nutrient Cycling and the Productivity of Humid Tropical Forests
The first Europeans to view humid tropical forests were stunned by the luxuriant growth, giant trees with huge buttresses, thick vines, plants growing on plants (epiphytes), and so forth. Such luxurious growth signals high productivity, and modern scientific measurements confirm this. If one measures the photosynthesis, or captures the litterfall of leaves, branches, fruit and other plant parts to the forest floor, one finds the production of tropical evergreen forests to be roughly double that of temperate forests. It would be natural to infer that tropical soils are very fertile in order to support this high productivity. But, as we have seen in other instances, or general inferences about what makes sense are often incorrect -- we must look more closely at the system and analyze how it functions. In fact the soils are very thin and the rock below them highly weathered (Figure 4). You already know that ecosystems are open with respect to nutrient cycling, meaning that inputs and outputs are significant. What makes humid tropical forests so productive is the combination of high temperatures, light, and rainfall year-round (good growing conditions), coupled with especially efficient nutrient recycling.
What is the evidence for this claim?
First, analysis of soils of tropical regions shows them to be virtually devoid of soluble minerals. Rocks weather rapidly due to high temperatures and abundant moisture, and millennia of rapid weathering and torrential rains to wash away nutrients from the soils have left the soils very low in nutrient stocks. This is supported by the analysis of stream water draining tropical regions, which likewise reveals a scarcity of dissolved nutrients. Most tropical soils are clays with little soluble mineral content, and moderate to strong acidity which interferes with the ability of roots to take up nutrients. Only about 20% of the humid tropics has soils that can support agriculture, and most of this area is already in use.
If the nutrients aren't in the soils, where do they come from?
Figure 5 shows a budget accounting that indicates nutrients are found mainly in living plant biomass and in the layer of decomposing litter; there is little nutrient content of the deeper soil, as there is in temperate-zone ecosystems. This suggests that plants are intercepting and taking up nutrients the moment they are released by decomposition. There are many organisms that are players in this decomposition process: termites, bacteria, fungi, various invertebrates. Of particular importance are micorrhizal fungi which invade the roots of trees to obtain nourishment. As we learned in the lecture on Microbes, these fungi gain carbon nourishment from the tree and they benefit the tree by providing a vastly expanded nutrient gathering network in the soils. In some circumstances tree roots even grow upward toward the soil surface, permeating the litter layer. Isotope experiments have shown the importance of roots in nutrient uptake. For example, one study in the Amazon rain forest, which used Ca-45 and P-35, found that more than 99% of the nutrients added to the system (in the form of isotopes) were retained in root mats. More commonly, about 60 - 80% of nutrients are retained by the roots, and thus made available to the tree. The remaining 20 - 40% needed by the tree must be made up by fresh inputs, either from rainfall or rock weathering. What happens when the forest is harvested for timber or other plant products, or the forest is burned? In all these cases nutrients will be lost from the ecosystem, but the outputs cannot exceed inputs for very long because the stock of nutrient capital in the system will be depleted. When forests are burned, or the cut timber is removed as in logging, the nutrients that were in the tree biomass are either washed out in the case of burning or simply removed from the system. Because there was only a small stock of nutrients in the soil and most of the nutrients were in the biomass, there is little nutrient stock remaining to support regrowth. This is why slash and burn agriculture does not work for more than a few years after burning, and why the land is made very infertile and growing new vegetation is difficult. We can't simply "regrow" tropical forests once they are burned -- once they are lost they are gone forever (or at least for 1000s of years, and even then the species that regrow will be different from the original forest species). Table 1 shows 7 tropical forests, arranged roughly from least to most fertile soils. Note the range of above-ground biomass is about twofold. Yet the nutrient stocks vary by several orders of magnitude (an "order of magnitude" is equal to one power of ten, so that 100 is one order of magnitude greater than 10, and 1000 is two orders of magnitude greater than 10). The greatest above-ground productivity is in the Ivory Coast forest, on soils of intermediate fertility. This reinforces the point that you cannot guess the fertility of the soils of a tropical forest by looking at the trees. Look next at the root biomass, which correlates pretty well with the soil fertility. Root biomass is highest where soil quality is poorest, and vice-versa. There is also a "causal" explanation for this correlation; when soil nutrients are high, the tree does not need to spend as much energy in building roots to forage in the soil for new nutrient sources. Competition for nutrients presumably is very strong at the Venezuelan sites with low soil fertility and high root biomass, whereas competition for light presumably is most important in the Ivory Coast forest. At the Venezuelan sites we also see a well developed surface root mat infiltrating the litter. We also see tougher, more slowly decaying leaves at the poor fertility sites. This is because leaves are held longer under poor growth conditions (their turnover time is longer), and because they are exposed to herbivores longer they must be better protected (meaning they need to be tough and unpalatable). This causes slow decomposition of the leaves once they are dropped to the forest floor, and further retards the forest's productivity.
Biodiversity
Tropical forests, covering 7% of the earth's surface area, contain perhaps 50% of the world's species. What causes this prodigious concentration of biological diversity? Until ten years ago, if you had asked any biologist how many species of plants and animals lived on earth, the answer probably would have been "about 2 million." This would include the nearly 1.5 million described species, and allowed for another half million un-described species.
Then, in 1982, Smithsonian biologist Terry Erwin developed a technique to fumigate the crowns of individually selected forest trees with biodegradable pyrethrin (the same chemical in mosquito coils). A huge number of previously unknown spiders, insects, and other invertebrates came tumbling down onto tarps spread on the forest floor. Based on the high proportion of undescribed species, and the expectation that each tree species contains many host-specific species (species that live only in that host tree), our estimates of biological diversity have been drastically altered. One commonly hears the figures of 5 to 30 million species, but the truth is we don't know. In fact, we know more about the stars in the sky than we do about the species on earth. We are certain that tropical forests contain a great many species, and most of these are unknown to science. We also know that the tropics are highly diverse based on evidence from well-studied groups, including the vertebrates and flowering plants. Whenever one compares the number of species along a latitudinal gradient (Figure 6), one observes a trend of increasing numbers of species towards the equator. Why are tropical forests so diverse? We only have partial answers. One class of answers centers around the spectacular specialization we observe in tropical forests. Tropical species exhibit highly specialized ecological roles. However, this begs the question of how these species became so specialized and diverse, and here we turn to an evolutionary perspective. First, let's examine two examples of the high degree of specialization found in tropical forests. The forests themselves are multi-layered. A temperate forest usually has two or three main layers. In an undisturbed forest the trees are fairly similar in height, there usually is some ground vegetation, and in between there may or may not be a shade-adapted middle layer. But tropical forests are vertically more complex (Figure 7). As many as perhaps five layers exist, although the distinctness of layers is arguable.
We also see evidence of great ecological specialization, as illustrated for mammals living in trees and on the ground which are active at day versus at night (Figure 8). The term "guild" is used much as it is in human society, to describe a collection of individuals who make a living in the same way. Human examples include cobblers, brewers, and professors. In the animal kingdom we use the word guild to indicate a finer sub-division than trophic level. As Figure 9 illustrates for birds, there are more guilds in the tropics than in the temperate zone, and more species per guild. Let's now turn to the deeper question of how this greater specialization came about. Although we don't fully understand why more species are formed in one place than another, we do know that geographical isolation of small populations for a long time promotes species formation (refer back to the Lecture on The Process of Speciation). This is because those isolated populations become independent genetic and hence independent evolutionary units. If the gene pool is small and the environment is unique, evolutionary specialization is likely. It also seems likely that the forests of the tropics have gone through many cycles of fragmentation and reunion, due to the same global climate changes that gave us repeated bouts of glaciations at higher latitudes. These repeated episodes of forest retreat and advance would provide numerous opportunities for forest-dwelling species to be isolated into separate small populations. This in turn allows genetic change and evolutionary specialization to occur. The reasoning goes as follows. The border between forest and non-forest in present-day tropical South America closely follows the line of 1500 mm annual precipitation.
During periods of glaciation, the earth's average temperature was cooler, and this would result in less evaporation and thus less rainfall. During these dry periods, the area receiving more than 1500 mm of rainfall would be reduced and fragmented.
During wetter periods associated with interglacials (time during the glacial retreats), forests would expand and rejoin. If the dry periods correspond roughly to periods of glacial advance, they would have lasted 50 to 100 thousand years, which likely is sufficient time for evolutionary divergence. This process has happened over and over, in conjunction with the many cycles of glaciation that the earth has experienced in the last several million years. Therefore the Milankovitch cycles , which drive much of the glacial activity, may have acted as a "species pump", causing the process of speciation to be more active in the tropics and resulting in more species found there today. Now, we must also remember that this idea is speculation because we cannot demonstrate the process in experiments and we can't go back in a time machine to observe the process directly. However, the process does correspond well to what we know about the causes of species formation, and how climate influences the distribution of dominant vegetation. Some other factors probably contribute to the rich specialization of tropical rain forests. Two of the favored candidate factors are high year-round productivity, and the lack of any need to adapt to harsh environment conditions. In addition, specialization may favor further specialization, in a kind of runaway cycle.
Human Use and Sustainability
Tropical forests once covered 15-20% of earth's land surface. About half of this is now replaced by cropland, pasture, tree plantations, secondary forest, or wasteland. We are in a race between human destruction and human discovery. Some say we have less than 50 years before we'll hit bottom, with perhaps only 5-10% of tropical forests remaining. Why are we rapidly converting these lush, productive, and biologically diverse ecosystems to agriculture? Clearly, this is to meet the needs for food and land of the rapidly growing number of peasant farmers in tropical countries. Equally clearly, there is a need to meet this demand. The question is, are we doing so in a sensible way? Ecosystem science gives us a basis to evaluate this aspect of change now occurring on a global scale, using the criteria of productivity and ecological sustainability. The two primary categories of disruption that result from the conversion of tropical rainforests to agricultural land concern nutrient and water cycles.
1. Disruption of nutrient cycles.
Traditional slash and burn agriculture releases the nutrients held in above ground biomass to produce a high yield from a small area right after the burning. Afterwards, such areas are left fallow (unused) for years to decades because the nutrients have been mostly lost from the system, as described earlier in this lecture. This traditional land use is not really "sustainable" because the majority of the land is fallow at any one time and new areas of forests must be cut and burned. Alternatives to this agricultural system are highly debatable. There have been some spectacularly unsuccessful efforts to adapt modern agriculture from the temperate zone to tropical conditions. Without fertilizers, crop yields decline each year as the remaining nutrients in the soil are further depleted. Mechanization and fertilizers usually produce high yields, but the rate of soil erosion and degradation indicate that these practices are not sustainable into the future. High-tech agriculture also is costly and requires a level of technological sophistication that is inconsistent with the low-tech needs of rural agriculture. As a consequence, many people regard such efforts with great skepticism. However, research continues, and solutions would benefit people and simultaneously relieve some of the pressures on remaining wildlands.
2. Disruption of the water cycle
Not just nutrients are lost when the forest is removed. The water cycle itself is disrupted, and the initial consequence is increased erosion because there is no vegetation to act as a "buffer" to hold the water in the plants and soils. Another likely consequence is a long-term and irreversible decline in available water in the region. Initially in this lecture, we emphasized how climate determined the type of ecosystem in any tropical area, and thus its productivity. Here we see that ecosystems influence climate in the form of a feedback through the water cycle. An area as vast as the Amazonian rain forest recycles a great deal of rainfall back into the atmosphere by transpiration. If the forest is removed, that precipitation will run off to the sea via river flow, as has been demonstrated in many experiments where forests are clear cut. Evaporation of sea water will of course return fresh water to the atmosphere, but it is very unlikely that the Amazon rain forest will receive much of the rainfall. The climate of the Amazon region will become drier, and it is questionable whether a humid tropical forest would ever be able to re-establish. This inference is supported by a computer model in which the Amazonian forest was replaced by grasslands due to land use change. Surface temperatures increased in the model, evapotranspiration declined, and precipitation also declined. It appears that a dry season would occur, sufficient to prevent the re-establishment of a humid forest. ===Summary===
Tropical rain forests are found in regions where temperatures and precipitation are high year-round
High primary productivity in tropical rain forests is due to the combination of climate and efficient recycling of nutrients through plant biomass
Tropical rain forests may contain 50% or more of the world's biodiversity. High biodiversity appears related to high ecological specialization of species.
Periods of forest fragmentation in the past, driven by global changes in climate such as glacial cycles, may have led to high rates of speciation due to geographic isolation.
Tropical rain forests are being converted to agricultural land, with associated erosion and disruptions of nutrient and water cycling.
Deforestation (cutting down trees) is a major problem caused by humans in the tropical rainforest. Global Rates of Deforestation:
2.47 acres (1 hectare) per second: equivalent to two U.S. football fields
150 acres (60 hectares) per minute
214,000 acres (86,000 hectares) per day: an area larger than New York City
78 million acres (31 million hectares) per year: an area larger than Poland
The image below shows some of the causes and effects of deforestation in the Amazon Rainforest. Place you mouse over the image to discover the causes. Click to view information on each factor. Slash and burn
Most clearances are still by the local people and tribes needing land on which to grow crops. They clear the forest by ‘slash and burn’. Vegetation is cut down and then burned. The ash acts like a fertiliser adder nutrients to the soil. When the soil begins to turn infertile (usually after 3-5 years) the people move on. This is called shifting cultivation. It is a sustainable method of farming in the rainforest. It ensures the forest will recover. Road Building
The Transamazon Highway has allowed increased access to the Amazon Rainforest. Logging
Commercial logging is the major cause of primary rainforest destruction in South East Asia and Africa. World wide, it is responsible for the destruction of 5 million ha. per year. Logging roads enable landless people to enter the forest. In Africa, 75% of land being cleared by peasant farmers is land that has been previously logged. Cattle Ranching
Ranching is a major cause of deforestation, particularly in Central and South America. In Central America, two-thirds of lowland tropical forests have been turned into pasture since 1950. Hydroelectric Power
An unlimited supply of water and ideal river conditions have led to the development of hydro electric power stations (HEP Stations). Farming
There are nearly 3 million landless people in Brazil alone. The government has cleared large areas of the Amazon Rainforest and encouraged people to move there. The scheme has not been successful. Farmers stay on the same land and attempt to farm it year after year. Nutrients in the soil are quickly exhausted as there is no longer a humus layer to provide nutrients. The soil becomes infertile and nothing will grow. Mining
The mining of iron ore, bauxite , gold, oil and other minerals have benefited many LEDCs. However, it has also devastated large areas of rainforest e.g. The Amazon. Deforestation is causing many problems at a range of scales: Local: Ecosystem
About 80% of the rainforests nutrients comes from trees and plants. That leaves 20% of the nutrients in the soil. The nutrients from the leaves that fall are instantly recycled back up into the plants and trees. When a rainforest is clear-cut, conditions change very quickly. The soil dries up in the sun. When it rains, it washes the soil away. The rainforest never fully recovers. Wildlife and plant life is reduced.
Elimination of Indian groups and their way of life
Estimates suggest that 80% of forest Indians have died since the arrival of Europeans in the sixteenth century. Most have died from western diseases such as malaria to which they have no immunity. Those remaining have been forced away by the construction of roads, ranches, mines and reservoirs
Soil Erosion
When vegetation is removed soil is left exposed to the heavy equatorial rainfall. It is rapidly eroded. The removal of top soil means little vegetation will grow. Also, soil erosion leads to flooding as soil is deposited on river beds.
National: Deforestation can consume a country's only natural resource. If deforestation is not managed in a sustainable manner a country's only natural resource could be lost forever. Global: Global Warming
Rainforest canopies absorb carbon dioxide which is a gas in the atmosphere. When the rainforests are burned and cleared, the carbon is released. Also, when trees are cut down they can no longer absorb carbon dioxide. This means more carbon dioxide is in the atmosphere. Carbon dioxide allows heat through the atmosphere (suns rays). However, it will not allow reflected energy to escape from the atmosphere. This is called the greenhouse effect and causes global warming. If development in the rainforest is to be sustainable (e.g. although the resources are used to aid development, it/they will still exist for future generations to use) a number of measures must be taken. These include: Afforestation - Trees should be replanted in areas of deforestation. Shifting Cultivation - Farmers should move on after 2-3 years to allow the rainforest to recover. Rubber tapping - More sustainable methods of exploiting the rainforest should be pursued e.g. rubber tapping Measuring trees - Trees should only be cut down when they reach a certain size. This will ensure younger trees survive longer and will encourage careful management of the rainforest.
MAX'S WORK (I ROCK)
1)http://www.forestethics.org/
-Covers ABCD and E
Very broad...
-Touches on A,B,C
Tropical Rainforests: Equatorial Forests of Rain
Of all the world's forests, it is those in the tropics that face the greatest threat from mankind. Tropical rainforests are one of nature's treasures, and many of them are now at risk. We have already destroyed half of the world's original tropical rainforests! Just in a few decades, we can possibly witness the complete elimation of the world's rainforests. The biodiversity of this biome is legendary -- this biome contains the largest biomass. Did you know that enough rainforests are being destroyed every minute to fill 50 football fields? We need to preserve these valuable resources because they are the lungs of our planet, and can possibly hold cures for many of our most deadly diseases. The tropical rainforests are a critical link in the ecological chains of our our earth's biosphere. To learn more interesting facts about the tropical rainforests, please visit our Did you know? section.
Generally, there is a flow of air that comes from the poles of the Earth, towards the equator. These winds are filled with moisture and the intense heat that is located at the equator causes the moisture to rise, cool and then condense to create rain. This continuous cycle causes it to rain almost 24 hours a day around most of the tropical areas. In some regions there can be more than 15 feet of rain a year. There are one or more "dry" months in this tropical biome, however if one would visit they would see it still is astonishingly wet.
Within a four mile square area of a tropical rainforest, you would find: * Over 750 species of trees
- 1500 different kinds of flowering plants
- 125 species of mammals
- 400 species of birds
- 100 reptiles
- 60 amphibians
- countless insects
- 150 species of butterflies
Only 1% of these species has ever been studiedOther Internet Resources:
3)http://www.nature.org/rainforests/
-Touches on A,B,E
You can Adopt an Acre of rainforest and help to protect Costa Rica's breathtaking Osa Peninsula now and for future generations.
Rainforests of the World
Wild and wondrous, rainforests extend from as far as Alaska and Canada to Latin America, Asia and Africa. They nurture thousands of plants and animals found nowhere else on Earth and provide life's essentials such as our medicines, food and water.The Nature Conservancy is working around the world in places like Costa Rica's Osa Peninsula to protect rainforests, engaging local and indigenous communities in creative solutions that balance the needs of people with nature.
The places and projects featured on this site reflect examples of The Nature Conservancy's current work in rainforest protection. And every year, through our Adopt an Acre® program, we choose an imperiled rainforest site that is in critical need of protection.
Why Should You Care About the Rainforest?
Besides providing food, water and air to the rest of the world, rainforests offer critical habitat for many of the Earth's most interesting and rare plants and animals. Read on for more rainforest facts:The Nature Conservancy's Rainforests Work
The Nature Conservancy has launched many conservation programs to protect these vital forests and all the plants, animals and people that depend on them. Working in many of the world's most threatened forest systems, The Nature Conservancy has had many tangible and lasting successes:- Plant and animal diversity assessments of the coastal Amazon rainforest;
- Training for national park guards in Bolivia;
- Support for implementing rainforest protection projects in the Asia Pacific region;
- Sustainable income-generating projects in Chile;
- Effective park management in Panama and Costa Rica;
- Scientific analysis of new protected areas within temperate rainforests in Canada; and
- Since its beginning, our Adopt an Acre® program has protected hundreds of thousands of forested acres worldwide.
As some of the last truly wild places left in the world, rainforests deserve our immediate attention. You can help preserve the world's rainforests and the local communities around them when you adopt an acre of rainforest today.How Can You Help Save the Rainforest?
We are all part of this Earth. Invest in our future and the future of our planet. Be a steward of the rainforests.When you make a gift to protect the rainforest, you'll help to ensure that the world’s most vital forests like the Osa are restored, protected and sustained for future generations.
4)http://www.ehow.com/how_2163920_conserve-rainforest.html
- Does not touch on A,B,C,D or E but instead teaches u how to conserve rainforests.
Conserve the Rainforest by Recycling
- Step 1
Buy paper made from recycled materials. There's really no need to do otherwise, as recycled paper is available everywhere. Recycled paper often costs no more than regular paper.- Step 2
Participate in any recycling programs your local government has implemented. Place two garbage cans in your kitchen and encourage the family to sort recyclable paper products from general garbage. Your local waste management department may supply homes with special outdoor garbage cans for disposing of recyclable materials.- Step 3
Encourage recycling at your office. Talk to management about supplying recycling bins in addition to garbage cans. Circulate an office memo concerning conservation and recycling efforts.Reduce Paper Usage to Save the Rainforest
- Step 1
Turn to online news sources instead of printed hard copies of newspapers. Experts estimate that 30 million trees are cleared each year solely for the production of newspapers. Much of the trees used for newspapers come from tropical rainforest sources.- Step 2
Build a new home from materials other than trees. While American homes have been built from trees for generations, this has more to do with tradition than necessity. It's possible to build a home with little or no wood by using cob, rammed earth or PSP building techniques.- Step 3
Limit the amount of beef in your diet. It's estimated that 55 square feet of forest must be cleared to produce a single quarter-pound burger. While many fast food chains boast that they only use U.S. beef, the USDA only effectively labels where beef is processed and not where it's raised.- Step 4
Blow your nose into a washable handkerchief instead of tissue papers. Likewise, use towels and rags to clean your home instead of wasteful paper towels. Sacrifice a little convenience to help conserve our planet's rainforests.Reuse Paper Whenever Possible
- Step 1
Hang onto old pieces of junk mail. While you can't stop companies from wasting trees to produce ads that nobody reads, you can still put the paper to good use. Use old envelopes from credit- Step 2
Wrap your Christmas presents in old newspapers. While colorful, shiny wrapping paper has been associated with the birth of Christ during modern times, there's no practical or Biblical justification for the practice. Use the Christmas season as an opportunity to help conserve our planet's precious natural resources.5)http://www.wcupa.edu/aceer/rainforest.asp
- Touches on B, C, D, and E
Why Are Tropical Rainforests Important?
Tropical rainforests are the oldest and certainly the most complex ecosystems on our planet. They influence wind, rainfall, humidity and temperature patterns, and are a crucial link in the ecological chain of life—recycling water, oxygen, and carbon dioxide, and reducing soil erosion, flooding, and air contamination on a global scale.
Tropical rainforests play other important roles in our daily lives. Estimated to house almost half of the world’s plant, animal, and insect life, the forests are the Earth’s primary gene pool from which foods, medicine, and other products for the industrialized world are derived including coffee, tea, sugar, pepper, spices, bananas, rubber, and oils. Tropical rainforest plants already provide one-quarter of today’s pharmaceuticals and, according to The National Cancer Institute, a full 70% of the plants useful in the treatment of cancer are to be found only in our disappearing rainforest.
How Much Rainforest Remains?
Tropical rainforest is disappearing faster than any other natural community on Earth. If we continue at our current rate of destruction, with population being the dominant factor, 70% of our remaining rainforests will by gone by the year 2050! Ancient forests, some of which have existed intact for seventy million years, since the days of the dinosaurs, will all but vanish.
How Is The Rainforest Being Destroyed?
Why Won't The Rainforest Grow Back?
The complex and delicate relationships that have evolved over millions of years do not allow for independent survival. If the ecosystem of the world’s rainforest is destroyed, the stunning variety of plant and animal life we see today might never again regenerate. Without this complex system thriving above the soil, without nourishment from the roots and leaves of trees, the rainforest soil quickly becomes infertile. Crops planted on newly cleared land fail within a few years. Grasses planted for cattle refuse to seed and grow again. Without shade from the trees the earth is left dry, surrounding land flood from silt, and an eroded wasteland, emptied of the greatest diversity of life on Earth, is all that remains.
Some tribes, well acquainted with the rainforest and its many resources, are disappearing from the forest due to outside influences new to the rainforest people. Foreign diseases and viruses, to which the forest people may have little resistance, can sweep through a tribe with devastating results. Tribal forest land is lost to loggers, ranchers, miners, and pioneer settlers who arrive in the forest with little understanding of the traditional agricultural methods that have sustained the tribes for centuries. Without their land, the forest people are absorbed into the new, dominant culture. With the disintegration of cultural identity, the tribe and all its working knowledge of the rainforest are swiftly lost. The people and their culture become extinct.
What Are The Global Effects Of Deforestation?
The rainforest plays an integral support role for the planet. We know that on a regional basis deforestation results in soil loss, floods, drought, severe climatic changes, and the loss of a rich and bountiful habitat. We know also that the destruction of our tropical rainforest destroys the greatest storehouse of genetic diversity on Earth, a diversity that can provide new foods and medicines for the entire world. On a broader basis, the burning of the forests has been linked to increased carbon dioxide levels in our atmosphere, second only to that produced by the burning of fossil fuels. This well-documented increase in carbon dioxide levels is also associated with garbage dumping, changes in global climatic patterns, rising sea levels, and depletion of the protective ozone layer due to overpopulation. Consequently, action is needed now to protect what remains in our world’s rainforests. It is an important step toward the preservation of our future.
Edgar's work
Text 1: Answering point a).
A tropical rainforest is an ecosystem usually found around the equator. They are common in Asia, Australia, Africa, South America, Central America, Mexico and on many of the Pacific Islands. Within the World Wildlife Fund's biome classification, tropical rainforests are considered a type of tropical wet forest (or tropical moist broadleaf forest) and may also be referred to as lowland equatorial evergreen rainforest. Minimum normal annual rainfall between 1,750 millimetres (69 in) and 2,000 millimetres (79 in) occurs in this climate region. Mean monthly temperatures exceed 18 °C (64 °F) during all months of the year.[1] Rainforests are home to half of all the living animal and plant species on the planet.[2] Tropical rain forests are called the "world's largest pharmacy" because over one-quarter of modern medicines originate from its plants.[3] The undergrowth in a rainforest is restricted in many areas by the lack of sunlight at ground level.[4] This makes it possible for people and other animals to walk through the forest. If the leaf canopy is destroyed or thinned for any reason, the ground beneath is soon colonized by a dense tangled growth of vines, shrubs and small trees called a jungle.
This was received from http://en.wikipedia.org/wiki/Tropical_rainforest.
Text 2: Answering point b).
Tropical rainforests are unable to support human populations.[11] Food resources within the forest are extremely dispersed due to the high biological diversity and what food does exist is largely restricted to the canopy and requires considerable energy to obtain. Some groups of hunter-gatherers have exploited rainforest on a seasonal basis but dwelt primarily in adjacent savanna and open forest environments where food is much more abundant. Other peoples described as rainforest dwellers are hunter-gatherers who subsist in large part by trading high value forest products such as hides, feathers, and honey with agricultural people living outside the forest.[11]
[edit] Conversion to agricultural land
With the invention of agriculture humans were able to clear sections of rainforest to produce crops, converting it to open farmland. Such people, however, obtain their food primarily from farm plots cleared from the forest [11][12] and hunt and forage within the forest to supplement this.
Agriculture on formerly forested land is not without difficulties. Rainforest soils are often thin and leached of many minerals, and the heavy rainfall can quickly leach nutrients from area cleared for cultivation. People such as the Yanomamo of the Amazon, utilise slash-and-burn agriculture to overcome these limitations and enable them to push deep into what were previously rainforest environments. However, these are not rainforest dwellers, rather they are dwellers in cleared farmland[11][13] that make forays into the rainforest and up to 90% of the typical Yanamomo diet comes from farmed plants.[14]
[edit] Cultivated foods and spices
Coffee, chocolate, banana, mango, papaya, macadamia, avocado, and sugarcane all originally came from tropical rainforest and are still mostly grown on plantations in regions that were formerly primary forest. In the mid-1980s and 90s, 40 million tons of bananas were consumed worldwide each year, along with 13 million tons of mangoes. Central American coffee exports were worth US$3 billion in 1970. Much of the genetic variation used in evading the damage caused by new pests is still derived from resistant wild stock. Tropical forests have supplied 250 cultivated kinds of fruit, compared to only 20 for temperate forests. Forests in New Guinea alone contain 251 tree species with edible fruits, of which only 43 had been established as cultivated crops by 1985.[15]
[edit] Pharmaceutical and biodiversity resource
Tropical rainforests are called "the world's largest pharmacy"[citation needed] because of the large amount of natural medicines discovered in rainforests that are derived from rainforest plants. For example, rain forests contain the "basic ingredients of hormonal contraception methods, cocaine, stimulants, and tranquilizing drugs" (Banks 36)[citation needed]. Curare (a paralyzing drug) and quinine (a malaria cure) are also found there.
[edit] Tourism
Tourism in tropical rainforests has increased over the years having both positive and negative effects.[citation needed] People travel both nationally and internationally to experience rain forests firsthand.
[edit] Positive Impacts Onset dates and prevailing wind currents of the southwest summer monsoon.
Despite the negative effects of tourism in the tropical rainforests, there are also several important positive effects.
* An increase in tourism has increased economic support, allowing more revenue to go into the protection of the habitat. Tourism can contribute directly to the conservation of sensitive areas and habitat. Revenue from park-entrance fees and similar sources can be utilised specifically to pay for the protection and management of environmentally sensitive areas. Revenue from taxation and tourism provides an additional incentive for governments to contribute revenue to the protection of the forest.
* Tourism also has the potential to increase public appreciation of the environment and to spread awareness of environmental problems when it brings people into closer contact with the environment. Such increased awareness can induce more environmentally conscious behavior. Tourism has had a positive effect on wildlife preservation and protection efforts, notably in Africa but also in South America, Asia, Australia, and the South Pacific.[16]
This website was also received from the one above.
Text 3: Answering point c).
The Disappearing Rainforests
· We are losing Earth's greatest biological treasures just as we are beginning to appreciate their true value. Rainforests once covered 14% of the earth's land surface; now they cover a mere 6% and experts estimate that the last remaining rainforests could be consumed in less than 40 years.
· One and one-half acres of rainforest are lost every second with tragic consequences for both developing and industrial countries.
· Rainforests are being destroyed because the value of rainforest land is perceived as only the value of its timber by short-sighted governments, multi-national logging companies, and land owners.
· Nearly half of the world's species of plants, animals and microorganisms will be destroyed or severely threatened over the next quarter century due to rainforest deforestation.
· Experts estimates that we are losing 137 plant, animal and insect species every single day due to rainforest deforestation. That equates to 50,000 species a year. As the rainforest species disappear, so do many possible cures for life-threatening diseases. Currently, 121 prescription drugs sold worldwide come from plant-derived sources. While 25% of Western pharmaceuticals are derived from rainforest ingredients, less that 1% of these tropical trees and plants have been tested by scientists.
· Most rainforests are cleared by chainsaws, bulldozers and fires for its timber value and then are followed by farming and ranching operations, even by world giants like Mitsubishi Corporation, Georgia Pacific, Texaco and Unocal.
· There were an estimated ten million Indians living in the Amazonian Rainforest five centuries ago. Today there are less than 200,000.
· In Brazil alone, European colonists have destroyed more than 90 indigenous tribes since the 1900's. With them have gone centuries of accumulated knowledge of the medicinal value of rainforest species. As their homelands continue to be destroyed by deforestation, rainforest peoples are also disappearing.
· Most medicine men and shamans remaining in the Rainforests today are 70 years old or more. Each time a rainforest medicine man dies, it is as if a library has burned down.
· When a medicine man dies without passing his arts on to the next generation, the tribe and the world loses thousands of years of irreplaceable knowledge about medicinal plants.
This text was received from http://www.rain-tree.com/facts.htm.
Text 4: Answering point a).
- The Amazon Rainforest covers over a billion acres, encompassing areas in Brazil, Venezuela, Colombia and the Eastern Andean region of Ecuador and Peru. If Amazonia were a country, it would be the ninth largest in the world.
- More than half of the world's estimated 10 million species of plants, animals and insects live in the tropical rainforests.
- One hectare (2.47 acres) may contain over 750 types of trees and 1500 species of higher plants.
This text was from the same source as above.
Text 5: Answering to point b).
- The Amazon Rainforest has been described as the "Lungs of our Planet" because it provides the essential environmental world service of continuously recycling carbon dioxide into oxygen. More than 20 percent of the world oxygen is produced in the Amazon Rainforest.
- One-fifth of the world's fresh water is in the Amazon Basin.
- At least 80% of the developed world's diet originated in the tropical rainforest. Its bountiful gifts to the world include fruits like avocados, coconuts, figs, oranges, lemons, grapefruit, bananas, guavas, pineapples, mangos and tomatoes; vegetables including corn, potatoes, rice, winter squash and yams; spices like black pepper, cayenne, chocolate, cinnamon, cloves, ginger, sugar cane, tumeric, coffee and vanilla and nuts including Brazil nuts and cashews.
- Rainforest plants are rich in secondary metabolites, particularly alkaloids. Biochemists believe alkaloids protect plants from disease and insect attacks. Many alkaloids from higher plants have proven to be of medicinal value and benefit.
- Currently, 121 prescription drugs currently sold worldwide come from plant-derived sources. And while 25% of Western pharmaceuticals are derived from rainforest ingredients, less than 1% of these tropical trees and plants have been tested by scientists.
- The U.S. National Cancer Institute has identified 3000 plants that are active against cancer cells. 70% of these plants are found in the rainforest. Twenty-five percent of the active ingredients in today's cancer-fighting drugs come from organisms found only in the rainforest.
- Vincristine, extracted from the rainforest plant, periwinkle, is one of the world's most powerful anticancer drugs. It has dramatically increased the survival rate for acute childhood leukemia since its discovery.
- In 1983, there were no U.S. pharmaceutical manufacturers involved in research programs to discover new drugs or cures from plants. Today, over 100 pharmaceutical companies and several branches of the US government, including giants like Merck and The National Cancer Institute, are engaged in plant research projects for possible drugs and cures for viruses, infections, cancer, and even AIDS.
This text was received from the same source as above.
Text 6: Answering to point d).
Due to their positioning in the monsoon regions of the Earth, the Rainforests attract heavy rainfall and absorb
large quantities of carbon dioxide and emit oxygen into the atmosphere. Due to the Earth’s tilt, the Rainforests are
situated in a region of the Earth that gets regular sunlight. As the rain falls in this region, it helps to cool the Earth. This in
turn causes a climate within a climate as the humidity creates moisture, which is condensed into clouds. The rains then
return to the forests to be taken up by the trees and plants. This cycle is ever repeating and it cools the Earth, and also
creates lush green environments in these areas.
To mention the Earth's tilt again. The Earth's tilt in axis of rotation is normally 23.5 degrees from the
perpendicular to the orbit plane. But the Earth's tilt is out by 5 more degrees causing instability within the core. If all of
the Rainforests are destroyed by 2012, then there is no way this error can be corrected. We must start replanting NOW to
stop the environmental catastrophe that will befall us.
The Rainforests have more of a role in balancing the Earth’s temperatures than we realise, both internally and
externally, controlling the Earth’s winds and believe it or not, the temperature of the Seas.
The Rainforests also keep the pattern of the winds to the northern and southern hemispheres. With the rainforests being
destroyed, these winds are changing their direction, spreading disease to other parts of the Earth and coupled with
warmer temperatures, the rain is unlikely to fall in sufficient quantities in the right places that would cool the Earth. These
areas would then be more prone to flash floods and mudslides. With changing wind patterns, the temperature of the seas
would not be able to be kept constant. The Earth maintains an equilibrium but our actions are hampering its
efforts !
Some scientists argue that these are natural changes and that there is nothing to worry about, but these
changes are the result of global warming and whether a natural occurrence or not, has most definitely been accelerated
by Man due to an increasing reliance on fossil fuels – It is reported by scientists that in the last 450,000 years,
carbon dioxide (produced from the combustion of fossil fuels) has not risen as much as it has since the
Industrial revolution!
This text was received from http://www.saveourearth.co.uk/downloads/leaflet.pdf.
Yu Tse's work
Website 1: http://www.fs.fed.us/global/lzone/student/tropical.htm
The world's tropical forests circle the globe in a ring around the Equator They are surprisingly diverse, ranging from lush rain forests to dry savannas and containing millions of species of plants and animals (fig. 1). Tropical forests once covered some 15.3 billion acres (6.2 billion ha). In recent times, however, they have been cut at a rapid rate to make room for agriculture and to obtain their many valuable products. Between 1985 and 1990, 210 million acres (85 million ha) of tropical forests were destroyed.
This guide shows how modern forest practices can help stem the tide of forest destruction while providing valuable forest products for people. The tropical forests of Puerto Rico, which were abused for centuries, were badly depleted by the early 1900's. Widespread abandonment of poor agricultural lands has allowed natural reforestation and planting programs to create a patchwork of private, Commonwealth, and Federal forests across the land (fig. 2). The most frequent example in this publication is the Luquillo Experimental Forest, which could be a model for protecting and managing tropical forests worldwide.
About half of all the world's forests are in the Tropics, the area between the Tropic of Cancer and the Tropic of Capricorn. This region may be best known for its rain forests - lush, steamy jungles with towering trees, epiphytes, and dense under stories of smaller trees, shrubs, and vines.
Tropical forests are surprisingly diverse. In addition to rain forests, there are mangroves, moist forests, dry forests, and savannas. Such classifications, however, give only a slight indication of the diversity of tropical forests. One study by the Food and Agriculture Organization (FAO) of the United Nations, which considered 23 countries in tropical America, 37 in tropical Africa, and 16 in tropical Asia, identified dozens of types of tropical forests: open and closed canopy forests, broadleaved trees and conifer forests , closed forests and mixed forest grasslands, and forests where agriculture has made inroads.
Rain Forests
The largest remaining areas of tropical rain forests are in Brazil, Congo, Indonesia, and Malaysia. Precipitation generally exceeds 60 inches (150 cm) per year and may be as high as 400 inches (1000 cm). Lowland rain forests are among the world's most productive of plant communities. Giant trees may tower 200 feet (60 m) in height and support thousands of other species of plants and animals. Montane (mountain) rain forests grow at higher elevations where the climate is too windy and wet for optimum tree growth.
Mangrove forests grow in the swampy, intertidal margin between sea and shore and are often considered part of the rain forest complex. The roots of mangrove trees help stabilize the shoreline and trap sediment and decaying vegetation that contribute to ecosystem productivity (fig. 3).
Dry Forests
Large areas of tropical dry forests are found in India, Australia, Central and South America, the Caribbean, Mexico, Africa, and Madagascar. Dry forests receive low rainfall amounts, as little as 20 inches (50 cm) per year, and are characterized by species well adapted to drought. Trees of dry tropical forests are usually smaller than those in rain forests, and many lose their leaves during the dry season. Although they are still amazingly diverse, dry forests often have fewer species than rain forests.
Savanna is a transitional type between forest and grassland. Trees are often very scattered and tend to be well adapted to drought and tolerant of fire and grazing. If fire is excluded, trees eventually begin to grow and the savanna is converted to dry forest. With too much fire or grazing, dry forest becomes savanna (fig. 4). This vegetation type has fewer species of trees and shrubs but more grasses and forbs than other forest types in the Tropics.
All forests have both economic and ecological value, but tropical forests are especially important in global economy. These forests cover less than 6 percent of the Earth's land area, but they contain the vast majority of the world's plant and animal genetic resources. The diversity of life is astonishing. The original forests of Puerto Rico, for example, contain more than 500 species of trees in 70 botanical families. By comparison, temperate forests have relatively few. Such diversity is attributed to variations in elevation, climate, and soil, and to the lack of frost.
There is also diversity in other life forms: shrubs, herbs, epiphytes, mammals, birds, reptiles, amphibians, and insects. One study suggests that tropical rain forests may contain as many as 30 million different kinds of plants and animals, most of which are insects (fig. 5).
Wood and Other Products
Tropical forests provide many valuable products including rubber, fruits and nuts, meat, rattan, medicinal herbs, floral greenery, lumber, firewood, and charcoal. Such forests are used by local people for subsistence hunting and fishing. They provide income and jobs for hundreds of millions of people in small, medium, and large industries.
Tropical forests are noted for their beautiful woods (fig. 6). Four important commercial woods are mahogany, teak, melina, and okoume. Honduras mahogany (Swietenia macrophylla), grows in the Americas from Mexico to Bolivia. A strong wood of medium density, mahogany is easy to work, is long lasting, and has good color and grain. It is commonly used for furniture, molding, paneling, and trim. Because of its resistance to decay, it is a popular wood used in boats. Teak (Tectona grandis) is native to India and Southeast Asia. Its wood has medium density, is strong, polishes well, and has a warm yellow-brown color. Also prized for resistance to insects and rot, teak is commonly used in cabinets, trim, flooring, furniture, and boats (fig. 7). Melina (Gmelina arborea) grows naturally from India through Vietnam. Noted for fast growth, melina has light colored wood that is used mainly for pulp and particleboard, matches and carpentry. Okoume (Aucoumea klaineana) is native to Gabon an the Congo in west Africa. A large fast-growing tree, the wood has mod erately low density, good strength-to density ratio, and low shrinkage during drying. It is commonly use( for plywood, paneling, interior fur niture parts, and light construction.
Other Economic Values
Tropical forests are home for tribal hunter-gatherers whose way of life has been relatively unchanged for centuries. These people depend on the forests for their livelihood. More than 2.5 million people also live in areas adjacent to tropical forests. They rely on the forests for their water, fuelwood, and other resources and on its shrinking land base for their shifting agriculture. For urban dwellers, tropical forests provide water for domestic use and hydroelectric power. Their scenic beauty, educational value, and opportunities for outdoor recreation support tourist industries.
Many medicines and drugs come from plants found only in tropical rain forests. Some of the best known are quinine, an ancient drug used for malaria; curare, an anesthetic and muscle relaxant used in surgery; and rosy periwinkle, a treatment for Hodgkin's disease and leukemia. Research has identified other potential drugs that may have value as contraceptives or in treating a multitude of maladies such as arthritis, hepatitis, insect bites, fever, coughs, and colds. Many more may be found. In all, only a few thousand species have been evaluated for their medicinal value.
In addition, many plants of tropical forests find uses in homes and gardens: ferns and palms, the hardy split-leaf philodendron, marantas, bromeliads, and orchids (fig. 8), to name just a few.
Environmental Benefits
Tropical forests do more than respond to local climatic conditions; they actually influence the climate. Through transpiration, the enormous number of plants found in rain forests return huge amounts of water to the atmosphere, increasing humidity and rainfall, and cooling the air for miles around. In addition, tropical forests replenish the air by utilizing carbon dioxide and giving off oxygen. By fixing carbon they help maintain the atmospheric carbon dioxide levels low and counteract the global "greenhouse" effect.
Forests also moderate stream flow. Trees slow the onslaught of tropical downpours, use and store vast quantities of water, and help hold the soil in place. When trees are cleared, rainfall runs off more quickly, contributing to floods and erosion.
Before the dawn of agriculture approximately 10,000 years ago, forests and open woodland covered about 15.3 billion acres (6.2 billion ha) of the globe. Over the centuries, however, about one-third of these natural forests has been destroyed. According to a 1982 study by FAO, about 27.9 million acres (11.3 million ha) of tropical forests are cut each year-an area about the size of the States of Ohio or Virginia. Between 1985 and 1990, an estimated 210 million acres (85 million ha) of tropical forests were cut or cleared. In India, Malaysia, and the Philippines, the best commercial forests are gone, and cutting is increasing in South America. If deforestation is not stopped soon, the world will lose most of its tropical forests in the next several decades.
Reasons for Deforestation
Several factors are responsible for deforestation in the Tropics: clearing for agriculture, fuelwood cutting, and harvesting of wood products. By far the most important of these is clearing for agriculture. In the Tropics, the age-old practice of shifting, sometimes called "slash-and-burn," agriculture has been used for centuries. In this primitive system, local people cut a small patch of forest to make way for subsistence farming. After a few years, soil fertility declines and people move on, usually to cut another patch of trees and begin another garden.
In the abandoned garden plot, the degraded soil at first supports only weeds and shrubby trees. Later, soil fertility and trees return, but that may take decades. As population pressure increases, the fallow (rest) period between cycles of gardening is shortened, agricultural yields decrease, and the forest region is further degraded to small trees, brush, or eroded savanna.
Conversion to sedentary agriculture is an even greater threat to tropical forests. Vast areas that once supported tropical forests are now permanently occupied by subsistence farmers and ranchers and by commercial farmers who produce sugar, cocoa, palm oil, and other products.
In many tropical countries there is a critical shortage of firewood. For millions of rural poor, survival depends on finding enough wood to cook the evening meal. Every year more of the forest is destroyed, and the distance from home to the forest increases. Not only do people suffer by having to spend much of their time in the search for wood, but so does the land. Damage is greatest in dry tropical forests where firewood cutting converts forests to savannas and grasslands.
The global demand for tropical hardwoods, an $8-billion-a-year industry, also contributes to forest loss. Tropical forests are usually selectively logged rather than clear-cut. Selective logging leaves the forest cover intact but usually reduces its commercial value because the biggest and best trees are removed. Selective logging also damages remaining trees and soil, increases the likelihood of fire, and degrades the habitat for wildlife species that require large, old trees-the ones usually cut. In addition, logging roads open up the forests to shifting cultivation and permanent settlement.
In the past, logging was done primarily by primitive means-trees were cut with axes and logs were moved with animals such as oxen. Today the use of modern machinery--chain saws, tractors, and trucks -makes logging easier, faster, and potentially more destructive.
Endangered Wildlife
Forests are biological communities-complex associations of trees with other plants and animals that have evolved together over millions of years. Because of the worldwide loss of tropical forests, thousands of species of birds and animals are threatened with extinction. The list includes many unique and fascinating animals, among them the orangutan, mountain gorilla, manatee, jaguar, and Puerto Rican parrot. Although diverse and widely separated around the globe, these specles have one important thing in common. They, along with many other endangered species, rely on tropical forests for all or part of their habitat.
Orangutans (Pongo pygmaeus) are totally dependent on small and isolated patches of tropical forests remaining in Borneo and Sumatra, Indonesia. Orangutans spend most of their time in the forest canopy where they feed on leaves, figs and other fruit, bark, nuts, and insects. Large trees of the old-growth forests support woody vines that serve as aerial ladders, enabling the animals to move about, build their nests, and forage for food. When the old forests are cut, orangutans disappear.
The largest of all primates, the gorilla, is one of man's closest relatives in the animal kingdom. Too large and clumsy to move about in the forest canopy, the gorilla lives on the forest floor where it forages for a variety of plant materials. Loss of tropical forests in central and west Africa is a major reason for the decreasing numbers of mountain gorillas (Gorilla gorilla). Some habitat has been secured, but the future of this gentle giant is in grave danger as a result of habitat loss and poaching.
The jaguar (Leo onca), a resident of the Southwestern United States and Central and South America, is closely associated with forests. Its endangered status is the result of hunting and habitat loss.
The Puerto Rican parrot (Amazona vittata), a medium-sized, green bird with blue wing feathers, once inhabited the entire island of Puerto Rico and the neighboring islands of Mona and Culebra. Forest destruction is the principal reason for the decline of this species. Hunting also contributed. Today, only a few Puerto Rican parrots remain in the wild and their survival may depend on the success of a captive breeding program (fig. 9).
In addition to species that reside in tropical forests year round, others depend on such forests for part of the year. Many species of migrant birds journey 1,000 miles or more between their summer breeding grounds in the north and their tropical wintering grounds. These birds are also threatened by tropical forest destruction.
Website 2: http://library.thinkquest.org/11353/trforest.htm
All the world's forests, it is those in the tropics that face the greatest threat from mankind. Tropical rainforests are one of nature's treasures, and many of them are now at risk. We have already destroyed half of the world's original tropical rainforests! Just in a few decades, we can possibly witness the complete elimation of the world's rainforests. The biodiversity of this biome is legendary -- this biome contains the largest biomass. Did you know that enough rainforests are being destroyed every minute to fill 50 football fields? We need to preserve these valuable resources because they are the lungs of our planet, and can possibly hold cures for many of our most deadly diseases. The tropical rainforests are a critical link in the ecological chains of our our earth's biosphere. To learn more interesting facts about the tropical rainforests, please visit our Did you know? section.
Generally, there is a flow of air that comes from the poles of the Earth, towards the equator. These winds are filled with moisture and the intense heat that is located at the equator causes the moisture to rise, cool and then condense to create rain. This continuous cycle causes it to rain almost 24 hours a day around most of the tropical areas. In some regions there can be more than 15 feet of rain a year. There are one or more "dry" months in this tropical biome, however if one would visit they would see it still is astonishingly wet.
Within a four mile square area of a tropical rainforest, you would find: * Over 750 species of trees
- 1500 different kinds of flowering plants
- 125 species of mammals
- 400 species of birds
- 100 reptiles
- 60 amphibians
- countless insects
- 150 species of butterflies
Only 1% of these species has ever been studiedWebsite 3: http://kids.mongabay.com/elementary/
Rainforests are important to the global ecosystem. Rainforests:
- provide a home to many plants and animals;
- help stabilize the world's climate;
- protect against flood, drought, and erosion;
- are a source for medicines and foods;
- support tribal people; and
- are an interesting place to visit
Rainforests help stabilize the world's climate by absorbing carbon dioxide from the atmosphere. Excess carbon dioxide in the atmosphere is believed to contribute to climate change through global warming. Therefore rainforests have an important in addressing global warming.Rainforests also affect local weather conditions by creating rainfall and moderating temperatures.
Rainforests help stabilize the world's climate by absorbing carbon dioxide from the atmosphere. Excess carbon dioxide in the atmosphere is believed to contribute to climate change through global warming. Therefore rainforests have an important in addressing global warming.
Rainforests also affect local weather conditions by creating rainfall and moderating temperatures.
Rainforests help maintain the water cycle. According to the U.S. Geological Survey, "the water cycle, also known as the hydrologic cycle, describes the continuous movement of water on, above, and below the surface of the Earth."
The role of rainforests in the water cycle is to add water to the atmosphere through the process of transpiration (where they release water from their leaves during photosynthesis). This moisture contributes to the formation of rain clouds which release the water back on the rainforest. In the Amazon, 50-80% of moisture remains in the ecosystem's water cycle.
When the forests are cut down, less moisture is goes into the atmosphere and rainfall declines and sometimes leads to drought.
The roots of rainforest trees and vegetation help anchor the soil. When trees are cut down there is no longer anything to protect the ground and soils are quickly washed away with rain. The process of washing away of soil is known as erosion.
As soil is washed down into rivers it causes problems for fish and people. Fish suffer because water becomes clouded, while people have trouble navigating waterways that are shallower because of the increased amount of dirt in the water. Meanwhile farmers lose topsoil that is important for growing crops.
Website 4: www.en.wikipedia.org
Habitation
Tropical rainforests are unable to support human populations.[11] Food resources within the forest are extremely dispersed due to the high biological diversity and what food does exist is largely restricted to the canopy and requires considerable energy to obtain. Some groups of hunter-gatherers have exploited rainforest on a seasonal basis but dwelt primarily in adjacent savanna and open forest environments where food is much more abundant. Other peoples described as rainforest dwellers are hunter-gatherers who subsist in large part by trading high value forest products such as hides, feathers, and honey with agricultural people living outside the forest.[11]
Conversion to agricultural land
With the invention of agriculture humans were able to clear sections of rainforest to produce crops, converting it to open farmland. Such people, however, obtain their food primarily from farm plots cleared from the forest [11][12] and hunt and forage within the forest to supplement this.
Agriculture on formerly forested land is not without difficulties. Rainforest soils are often thin and leached of many minerals, and the heavy rainfall can quickly leach nutrients from area cleared for cultivation. People such as the Yanomamo of the Amazon, utilise slash-and-burn agriculture to overcome these limitations and enable them to push deep into what were previously rainforest environments. However, these are not rainforest dwellers, rather they are dwellers in cleared farmland[11][12] that make forays into the rainforest and up to 90% of the typical Yanamomo diet comes from farmed plants.[12]
Cultivated foods and spices
Coffee, chocolate, banana, mango, papaya, macadamia, avocado, and sugarcane all originally came from tropical rainforest and are still mostly grown on plantations in regions that were formerly primary forest. In the mid-1980s and 90s, 40 million tons of bananas were consumed worldwide each year, along with 13 million tons of mangoes. Central American coffee exports were worth US$3 billion in 1970. Much of the genetic variation used in evading the damage caused by new pests is still derived from resistant wild stock. Tropical forests have supplied 250 cultivated kinds of fruit, compared to only 20 for temperate forests. Forests in New Guinea alone contain 251 tree species with edible fruits, of which only 43 had been established as cultivated crops by 1985.[13]
Pharmaceutical and biodiversity resource
Tropical rainforests are called "the world's largest pharmacy"[citation needed] because of the large amount of natural medicines discovered in rainforests that are derived from rainforest plants. For example, rain forests contain the "basic ingredients of hormonal contraception methods, cocaine, stimulants, and tranquilizing drugs" (Banks 36)[citation needed]. Curare (a paralyzing drug) and quinine (a malaria cure) are also found there.
Tourism
Tourism in tropical rainforests has increased over the years having both positive and negative effects.[citation needed] People travel both nationally and internationally to experience rain forests firsthand.
Positive Impacts
Onset dates and prevailing wind currents of the southwest summer monsoon.Despite the negative effects of tourism in the tropical rainforests, there are also several important positive effects.
- An increase in tourism has increased economic support, allowing more revenue to go into the protection of the habitat. Tourism can contribute directly to the conservation of sensitive areas and habitat. Revenue from park-entrance fees and similar sources can be utilised specifically to pay for the protection and management of environmentally sensitive areas. Revenue from taxation and tourism provides an additional incentive for governments to contribute revenue to the protection of the forest.
- Tourism also has the potential to increase public appreciation of the environment and to spread awareness of environmental problems when it brings people into closer contact with the environment. Such increased awareness can induce more environmentally conscious behavior. Tourism has had a positive effect on wildlife preservation and protection efforts, notably in Africa but also in South America, Asia, Australia, and the South Pacific.[14]
Ecosystem servicesIn addition to extractive human uses rain forests also have non-extractive uses that are frequently summarized as ecosystem services. Rain forests play an important role in maintaining biological diversity, modulating precipitation, infiltration and flooding, increasing scientific knowledge and in the spiritual well-being of humans. Such ecosystem services are of use to humans without the need for any modification or management of the forest yourself.
Website 5: http://www.savetherainforest.org/savetherainforest_007.htm
Often described as the Earth’s lungs, only in reverse, the tropical rainforests, take in vast quantities of carbon dioxide (a poisonous gas which mammals exhale) and through the process of photosynthesis, converts it into clean, breathable air. In fact, the tropical rainforests are the single greatest terrestrial source of air that we breathe.
What’s truly amazing, however, is that while the tropical rainforests cover just 2% of the Earth's land surface, they are home to two-thirds of all the living species on the planet. Additionally, "nearly half the medicinal compounds we use every day come from plants endemic to the tropical rainforest." If a cure for cancer or AIDS is to be found, it’ll almost certainly come from the tropical rainforests.
Norman Myers, in his book, The Primary Source, writes that "tropical rainforests are the Earth’s oldest continuous ecosystems. Fossil records show that the forests of Southeast Asia have existed in more or less their present form for 70 to 100 million years. The intensity of life forms is extraordinary: on the order of 1,000 species per square kilometer. By comparison, here in North America, we might only find 100 species in the same space." (2)
The largest rainforests are found in the Amazon Basin of South America, in Western African countries that skirt the equator, as well as South Pacific countries such as Indonesia and the Philippines. Smaller tracts of rainforests exist throughout Central America, parts of Mexico and Hawaii, as well as other islands of the Pacific and Caribbean.
Circling the Earth’s equator like a belt, the tropical rainforests maintain a near constant temperature of 80 degrees Fahrenheit and receive anywhere from 160 to 400 inches of rain per year. These favorable weather conditions allow all life forms to flourish year- round. Furthermore, by virtue of their location, the tropical rainforests were spared the extreme loss of life that characterized other regions of the globe during the ice ages. These two factors help explain why the tropical rainforests are home to between 50 and 70 million different life forms.
Tragically, the tropical rainforests are being destroyed at an alarming rate. According to Rainforest Action Network, more than an acre-and-a-half is lost every second of every day (refer to the entries below to see, quantitatively, what that translates into). That’s an area more than twice the size of Florida that goes up in smoke every year! "If present rates of destruction continue, half our remaining rainforests will be gone by the year 2025, and by 2060 there will be no rainforests remaining."
Every second . . we lose an area the size of two football fields!
Every minute . . we lose an area 29 times the size of the Pentagon!
Every hour . . . we lose an area 684 times larger than the New Orleans Superdome!
Every day . . . we lose an area larger than all five boroughs of New York City!
Every week . . . we lose an area twice the size of Rhode Island!
Every month . . .we lose an area the size of Belize!
Every year . . . we lose an area more than twice the size of Florida!
At the very least, "with the destruction of the tropical rainforests, over half the plant and animal species on earth, as well as numerous indigenous cultures will disappear forever."(2) If strong and decisive action is not taken immediately to reverse the destruction of this vital ecosystem, the consequences will be catastrophic. In fact, many scientists agree that the earth could very well become uninhabitable for virtually every living species, including humans!
We’ve consulted some knowledgeable experts in the field of tropical rainforest conservation and come up with some sobering facts that will lend credence for taking immediate action to save the last remaining tropical rainforests. And what might happen if we don’t.
B I O - D I V E R S I T Y
. . . "a typical four-mile square mile patch of rainforest contains as many as 1,500 species of flowering plants, 750 species of trees, 125 mammal species, 400 species of birds, 100 species of reptiles, 60 species of amphibians, and 150 different species of butterflies."
. . . "there are more fish species in the Amazon river system than in the entire Atlantic Ocean."
. . . "a single rainforest reserve in Peru is home to more species of birds than the entire United States."
. . . "at least 1/3 of the planet’s bird species live in the Amazon rainforest."
. . ."the Andean mountain range and the Amazon jungle are home to more than half of the world’s species of flora and fauna."
. . . "at least 1,650 rainforest plants can be utilized as alternatives to our present fruit and vegetable staples."
. . . "37% of all medicines prescribed in the US have active ingredients derived from rainforest plants."
. . . "70% of the plant species identified by the US National Cancer Institute as holding anti-cancer properties come from rainforests."
. . . "90% of the rainforest plants used by Amazonian Indians as medicines have not been examined by modern science."
. . . "of the few rainforest plant species that have been studied by modern medicine, treatments have been found for childhood leukemia, breast cancer, high blood pressure, asthma, and scores of other illnesses."
. . . "a hectare (2.471 acres) of rainforest absorbs one ton of carbon dioxide (CO2) per year."
. . . conversely, "the clearing and burning of the world’s rainforest accounts for 20-25% of the CO2 emitted into the atmosphere by man. It therefore could play a significant role in any so called "greenhouse effect" underway in our atmosphere."
THE COST OF RAINFOREST DESTRUCTION
. . . "almost half of the world’s original four billion acres of rainforest are now gone. The lost area equals the combined size of Washington, Idaho, California, Nevada and Arizona."
. . . "in 1500, there were an estimated six to nine million indigenous people inhabiting the tropical rainforests of Brazil. By 1900, that number had dropped to a million. Today, there are less than 250,000 indigenous people left in Brazil."
. . . "man has recently increased nature’s "normal" extinction rate by 10,000%. Most of this increase is taking place in the rainforests."
. . . "by conservative estimates, 9,000 species are going extinct each year, most of them from the rainforests."
. . . "we are presently experiencing the largest mass extinction since the demise of the dinosaurs 65 million years ago; only this time it’s occurring at a much faster rate."
Website 6: http://www.accu.or.jp/litdbase/material/pdf2/mt/mt09/mt09_06.pdf
Website 7: http://www.globalchange.umich.edu/globalchange1/current/lectures/kling/rainforest/rainforest.html
The Tropical Rain Forest
"... the most complex ecosystem on earth ... the tropical rain forest is one thousand times more biologically complex than the tropical reef system, the second most complex system on earth, with one million times greater biodiversity than our own ecosystem here." - Mike Robinson, Director of National Zoo Introduction
In previous lectures we focused on general principles of ecosystems, emphasizing the processes of biogeochemical cycling and energy transfers. In the next lectures we will look at one ecosystem in detail, the tropical forest. There are several reasons for this. Ecosystems may all function according to the same basic principles, but they most certainly don't all look the same and it is important to have some understanding and appreciation of this diversity. Second, it is important to learn about the "specifics" of ecosystems as well as the "generalities". Finally, we can use this examination of the tropical forest to help tie together some of the material that has been presented in the ecology and evolution sections of the course.Today we will examine the most productive and diverse ecosystem found on land: the tropical rain forest. These ecosystems are also, and perhaps more accurately, called humid tropical forests. These ecosystems are also changing rapidly, as Figure 1 illustrates in terms of the past and present distribution of tropical forests on earth.
Climate and Geography
Certain ranges of temperature and rainfall characterize the places where tropical rainforests occur:
Rainfall tends to be highest near the equator, where the sun's evaporative power causes high evapotranspiration, and rising air cools and then sheds its moisture. Precipitation tapers off as one moves away from the equator, and dry belts are found at 25-30 deg of latitude. Local variation can also be great due to trade winds, ocean currents, land masses, and mountain ranges.
Evergreen forests are replaced by deciduous forests as precipitation becomes seasonal. Wherever dry periods are several months or longer in duration, leaves are shed as the dry season takes hold, providing a winter-like visual appearance. Leaves re-appear in anticipation of or with the onset of the rains. (A dry month is one where evapotranspiration exceeds precipitation.) The growing season is thus shortened, and so forest productivity is less than in the evergreen forests of the more humid tropics. At lower annual rainfall (ca. 1500 mm), forest gives way to savanna as can be seen in the vegetation map of Africa in Figure 2.
Boundaries between ecosystems or biomes are often gradual, and they can be sensitive to changing conditions. A prolonged period of wetness or drought, or human intervention, can cause dramatic changes because of the transitional nature of environmental conditions near the boundaries between biomes.
Humid tropical forests appear superficially similar everywhere, but in fact they differ widely in species composition and ecosystem attributes. In the coterminous United States, botanists recognize 135 natural plant formations based on dominant species, and driven by latitude and climate. This system is called the Holdridge system (Figure 3) and it is widely used for conservation purposes. However, its use is far from feasible in tropics. Instead, the future in classifying tropical rainforest plant formations may lie in remote sensing, where large areas can be mapped relatively quickly.
Nutrient Cycling and the Productivity of Humid Tropical Forests
It would be natural to infer that tropical soils are very fertile in order to support this high productivity. But, as we have seen in other instances, or general inferences about what makes sense are often incorrect -- we must look more closely at the system and analyze how it functions. In fact the soils are very thin and the rock below them highly weathered (Figure 4).
You already know that ecosystems are open with respect to nutrient cycling, meaning that inputs and outputs are significant. What makes humid tropical forests so productive is the combination of high temperatures, light, and rainfall year-round (good growing conditions), coupled with especially efficient nutrient recycling.
What is the evidence for this claim?
First, analysis of soils of tropical regions shows them to be virtually devoid of soluble minerals. Rocks weather rapidly due to high temperatures and abundant moisture, and millennia of rapid weathering and torrential rains to wash away nutrients from the soils have left the soils very low in nutrient stocks.This is supported by the analysis of stream water draining tropical regions, which likewise reveals a scarcity of dissolved nutrients. Most tropical soils are clays with little soluble mineral content, and moderate to strong acidity which interferes with the ability of roots to take up nutrients. Only about 20% of the humid tropics has soils that can support agriculture, and most of this area is already in use.
If the nutrients aren't in the soils, where do they come from?
Figure 5 shows a budget accounting that indicates nutrients are found mainly in living plant biomass and in the layer of decomposing litter; there is little nutrient content of the deeper soil, as there is in temperate-zone ecosystems. This suggests that plants are intercepting and taking up nutrients the moment they are released by decomposition.
There are many organisms that are players in this decomposition process: termites, bacteria, fungi, various invertebrates. Of particular importance are micorrhizal fungi which invade the roots of trees to obtain nourishment. As we learned in the lecture on Microbes, these fungi gain carbon nourishment from the tree and they benefit the tree by providing a vastly expanded nutrient gathering network in the soils. In some circumstances tree roots even grow upward toward the soil surface, permeating the litter layer.
Isotope experiments have shown the importance of roots in nutrient uptake. For example, one study in the Amazon rain forest, which used Ca-45 and P-35, found that more than 99% of the nutrients added to the system (in the form of isotopes) were retained in root mats. More commonly, about 60 - 80% of nutrients are retained by the roots, and thus made available to the tree. The remaining 20 - 40% needed by the tree must be made up by fresh inputs, either from rainfall or rock weathering.
What happens when the forest is harvested for timber or other plant products, or the forest is burned? In all these cases nutrients will be lost from the ecosystem, but the outputs cannot exceed inputs for very long because the stock of nutrient capital in the system will be depleted. When forests are burned, or the cut timber is removed as in logging, the nutrients that were in the tree biomass are either washed out in the case of burning or simply removed from the system. Because there was only a small stock of nutrients in the soil and most of the nutrients were in the biomass, there is little nutrient stock remaining to support regrowth. This is why slash and burn agriculture does not work for more than a few years after burning, and why the land is made very infertile and growing new vegetation is difficult. We can't simply "regrow" tropical forests once they are burned -- once they are lost they are gone forever (or at least for 1000s of years, and even then the species that regrow will be different from the original forest species).
Table 1 shows 7 tropical forests, arranged roughly from least to most fertile soils. Note the range of above-ground biomass is about twofold. Yet the nutrient stocks vary by several orders of magnitude (an "order of magnitude" is equal to one power of ten, so that 100 is one order of magnitude greater than 10, and 1000 is two orders of magnitude greater than 10). The greatest above-ground productivity is in the Ivory Coast forest, on soils of intermediate fertility. This reinforces the point that you cannot guess the fertility of the soils of a tropical forest by looking at the trees.
Look next at the root biomass, which correlates pretty well with the soil fertility. Root biomass is highest where soil quality is poorest, and vice-versa. There is also a "causal" explanation for this correlation; when soil nutrients are high, the tree does not need to spend as much energy in building roots to forage in the soil for new nutrient sources. Competition for nutrients presumably is very strong at the Venezuelan sites with low soil fertility and high root biomass, whereas competition for light presumably is most important in the Ivory Coast forest. At the Venezuelan sites we also see a well developed surface root mat infiltrating the litter. We also see tougher, more slowly decaying leaves at the poor fertility sites. This is because leaves are held longer under poor growth conditions (their turnover time is longer), and because they are exposed to herbivores longer they must be better protected (meaning they need to be tough and unpalatable). This causes slow decomposition of the leaves once they are dropped to the forest floor, and further retards the forest's productivity.
Biodiversity
Tropical forests, covering 7% of the earth's surface area, contain perhaps 50% of the world's species. What causes this prodigious concentration of biological diversity?Until ten years ago, if you had asked any biologist how many species of plants and animals lived on earth, the answer probably would have been "about 2 million." This would include the nearly 1.5 million described species, and allowed for another half million un-described species.
We also know that the tropics are highly diverse based on evidence from well-studied groups, including the vertebrates and flowering plants. Whenever one compares the number of species along a latitudinal gradient (Figure 6), one observes a trend of increasing numbers of species towards the equator.
Why are tropical forests so diverse? We only have partial answers. One class of answers centers around the spectacular specialization we observe in tropical forests. Tropical species exhibit highly specialized ecological roles. However, this begs the question of how these species became so specialized and diverse, and here we turn to an evolutionary perspective.
First, let's examine two examples of the high degree of specialization found in tropical forests. The forests themselves are multi-layered. A temperate forest usually has two or three main layers. In an undisturbed forest the trees are fairly similar in height, there usually is some ground vegetation, and in between there may or may not be a shade-adapted middle layer. But tropical forests are vertically more complex (Figure 7). As many as perhaps five layers exist, although the distinctness of layers is arguable.
Let's now turn to the deeper question of how this greater specialization came about. Although we don't fully understand why more species are formed in one place than another, we do know that geographical isolation of small populations for a long time promotes species formation (refer back to the Lecture on The Process of Speciation). This is because those isolated populations become independent genetic and hence independent evolutionary units. If the gene pool is small and the environment is unique, evolutionary specialization is likely.
It also seems likely that the forests of the tropics have gone through many cycles of fragmentation and reunion, due to the same global climate changes that gave us repeated bouts of glaciations at higher latitudes. These repeated episodes of forest retreat and advance would provide numerous opportunities for forest-dwelling species to be isolated into separate small populations. This in turn allows genetic change and evolutionary specialization to occur.
The reasoning goes as follows. The border between forest and non-forest in present-day tropical South America closely follows the line of 1500 mm annual precipitation.
During periods of glaciation, the earth's average temperature was cooler, and this would result in less evaporation and thus less rainfall. During these dry periods, the area receiving more than 1500 mm of rainfall would be reduced and fragmented.
During wetter periods associated with interglacials (time during the glacial retreats), forests would expand and rejoin. If the dry periods correspond roughly to periods of glacial advance, they would have lasted 50 to 100 thousand years, which likely is sufficient time for evolutionary divergence. This process has happened over and over, in conjunction with the many cycles of glaciation that the earth has experienced in the last several million years. Therefore the Milankovitch cycles , which drive much of the glacial activity, may have acted as a "species pump", causing the process of speciation to be more active in the tropics and resulting in more species found there today.
Now, we must also remember that this idea is speculation because we cannot demonstrate the process in experiments and we can't go back in a time machine to observe the process directly. However, the process does correspond well to what we know about the causes of species formation, and how climate influences the distribution of dominant vegetation.
Some other factors probably contribute to the rich specialization of tropical rain forests. Two of the favored candidate factors are high year-round productivity, and the lack of any need to adapt to harsh environment conditions. In addition, specialization may favor further specialization, in a kind of runaway cycle.
Human Use and Sustainability
Tropical forests once covered 15-20% of earth's land surface. About half of this is now replaced by cropland, pasture, tree plantations, secondary forest, or wasteland. We are in a race between human destruction and human discovery. Some say we have less than 50 years before we'll hit bottom, with perhaps only 5-10% of tropical forests remaining.Why are we rapidly converting these lush, productive, and biologically diverse ecosystems to agriculture? Clearly, this is to meet the needs for food and land of the rapidly growing number of peasant farmers in tropical countries. Equally clearly, there is a need to meet this demand. The question is, are we doing so in a sensible way? Ecosystem science gives us a basis to evaluate this aspect of change now occurring on a global scale, using the criteria of productivity and ecological sustainability.
The two primary categories of disruption that result from the conversion of tropical rainforests to agricultural land concern nutrient and water cycles.
1. Disruption of nutrient cycles.
Traditional slash and burn agriculture releases the nutrients held in above ground biomass to produce a high yield from a small area right after the burning. Afterwards, such areas are left fallow (unused) for years to decades because the nutrients have been mostly lost from the system, as described earlier in this lecture. This traditional land use is not really "sustainable" because the majority of the land is fallow at any one time and new areas of forests must be cut and burned.Alternatives to this agricultural system are highly debatable. There have been some spectacularly unsuccessful efforts to adapt modern agriculture from the temperate zone to tropical conditions. Without fertilizers, crop yields decline each year as the remaining nutrients in the soil are further depleted. Mechanization and fertilizers usually produce high yields, but the rate of soil erosion and degradation indicate that these practices are not sustainable into the future. High-tech agriculture also is costly and requires a level of technological sophistication that is inconsistent with the low-tech needs of rural agriculture. As a consequence, many people regard such efforts with great skepticism. However, research continues, and solutions would benefit people and simultaneously relieve some of the pressures on remaining wildlands.
2. Disruption of the water cycle
Not just nutrients are lost when the forest is removed. The water cycle itself is disrupted, and the initial consequence is increased erosion because there is no vegetation to act as a "buffer" to hold the water in the plants and soils. Another likely consequence is a long-term and irreversible decline in available water in the region. Initially in this lecture, we emphasized how climate determined the type of ecosystem in any tropical area, and thus its productivity. Here we see that ecosystems influence climate in the form of a feedback through the water cycle. An area as vast as the Amazonian rain forest recycles a great deal of rainfall back into the atmosphere by transpiration. If the forest is removed, that precipitation will run off to the sea via river flow, as has been demonstrated in many experiments where forests are clear cut. Evaporation of sea water will of course return fresh water to the atmosphere, but it is very unlikely that the Amazon rain forest will receive much of the rainfall. The climate of the Amazon region will become drier, and it is questionable whether a humid tropical forest would ever be able to re-establish.This inference is supported by a computer model in which the Amazonian forest was replaced by grasslands due to land use change. Surface temperatures increased in the model, evapotranspiration declined, and precipitation also declined. It appears that a dry season would occur, sufficient to prevent the re-establishment of a humid forest.
===Summary===
Website 8: http://www.geography.learnontheinternet.co.uk/topics/rainforest.html
Deforestation (cutting down trees) is a major problem caused by humans in the tropical rainforest. Global Rates of Deforestation:
- 2.47 acres (1 hectare) per second: equivalent to two U.S. football fields
- 150 acres (60 hectares) per minute
- 214,000 acres (86,000 hectares) per day: an area larger than New York City
- 78 million acres (31 million hectares) per year: an area larger than Poland
The image below shows some of the causes and effects of deforestation in the Amazon Rainforest. Place you mouse over the image to discover the causes. Click to view information on each factor.Slash and burn
Most clearances are still by the local people and tribes needing land on which to grow crops. They clear the forest by ‘slash and burn’. Vegetation is cut down and then burned. The ash acts like a fertiliser adder nutrients to the soil. When the soil begins to turn infertile (usually after 3-5 years) the people move on. This is called shifting cultivation. It is a sustainable method of farming in the rainforest. It ensures the forest will recover.
Road Building
The Transamazon Highway has allowed increased access to the Amazon Rainforest.
Logging
Commercial logging is the major cause of primary rainforest destruction in South East Asia and Africa. World wide, it is responsible for the destruction of 5 million ha. per year. Logging roads enable landless people to enter the forest. In Africa, 75% of land being cleared by peasant farmers is land that has been previously logged.
Cattle Ranching
Ranching is a major cause of deforestation, particularly in Central and South America. In Central America, two-thirds of lowland tropical forests have been turned into pasture since 1950.
Hydroelectric Power
An unlimited supply of water and ideal river conditions have led to the development of hydro electric power stations (HEP Stations).
Farming
There are nearly 3 million landless people in Brazil alone. The government has cleared large areas of the Amazon Rainforest and encouraged people to move there. The scheme has not been successful. Farmers stay on the same land and attempt to farm it year after year. Nutrients in the soil are quickly exhausted as there is no longer a humus layer to provide nutrients. The soil becomes infertile and nothing will grow.
Mining
The mining of iron ore, bauxite , gold, oil and other minerals have benefited many LEDCs. However, it has also devastated large areas of rainforest e.g. The Amazon.
Deforestation is causing many problems at a range of scales:
Local:
Ecosystem
- About 80% of the rainforests nutrients comes from trees and plants. That leaves 20% of the nutrients in the soil. The nutrients from the leaves that fall are instantly recycled back up into the plants and trees. When a rainforest is clear-cut, conditions change very quickly. The soil dries up in the sun. When it rains, it washes the soil away. The rainforest never fully recovers. Wildlife and plant life is reduced.
- Elimination of Indian groups and their way of life
- Estimates suggest that 80% of forest Indians have died since the arrival of Europeans in the sixteenth century. Most have died from western diseases such as malaria to which they have no immunity. Those remaining have been forced away by the construction of roads, ranches, mines and reservoirs
Soil Erosion- When vegetation is removed soil is left exposed to the heavy equatorial rainfall. It is rapidly eroded. The removal of top soil means little vegetation will grow. Also, soil erosion leads to flooding as soil is deposited on river beds.
National:Deforestation can consume a country's only natural resource. If deforestation is not managed in a sustainable manner a country's only natural resource could be lost forever.
Global:
Global Warming
Rainforest canopies absorb carbon dioxide which is a gas in the atmosphere. When the rainforests are burned and cleared, the carbon is released. Also, when trees are cut down they can no longer absorb carbon dioxide. This means more carbon dioxide is in the atmosphere. Carbon dioxide allows heat through the atmosphere (suns rays). However, it will not allow reflected energy to escape from the atmosphere. This is called the greenhouse effect and causes global warming.
If development in the rainforest is to be sustainable (e.g. although the resources are used to aid development, it/they will still exist for future generations to use) a number of measures must be taken. These include:
Afforestation - Trees should be replanted in areas of deforestation.
Shifting Cultivation - Farmers should move on after 2-3 years to allow the rainforest to recover.
Rubber tapping - More sustainable methods of exploiting the rainforest should be pursued e.g. rubber tapping
Measuring trees - Trees should only be cut down when they reach a certain size. This will ensure younger trees survive longer and will encourage careful management of the rainforest.